[HKEY_LOCAL_MACHINE\SOFTWARE\Ipswitch\Network Monitor\WhatsUp Engine\Database Settings]
"DSN"="DSN=WhatsUp"
"CommandTimeout"=dword:0000003c
"DataSource_WhatsUp"="Persist Security Info=True;Initial Catalog=WhatsUp;Data Source=WHATSUP\\WHATSUP;Trusted_Connection=Yes"
"Username"="whatsup"
"Password"=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

[HKEY_LOCAL_MACHINE\SOFTWARE\Ipswitch\Network Monitor\WhatsUp Engine\Database Settings\Log Expiration Settings]
"Action Activity Log Expiration Time Limit (Hours)"=dword:00000000
"Active Discovery Log Expiration Time Limit (Hours)"=dword:00000000
"Performance Monitor Log Expiration Time Limit (Hours)"=dword:00000000
"General Error Log Expiration Time Limit (Hours)"=dword:00000000
"Passive Monitor Error Log Expiration Time Limit (Hours)"=dword:00000000
"Recurring Report Log Expiration Time Limit (Hours)"=dword:00000000
"System Activity Log Expiration Time Limit (Hours)"=dword:00000000
"Web User Activity Log Expiration Time Limit (Hours)"=dword:00000000
"Remote Server Log Expiration Time Limit (Hours)"=dword:00000000

[HKEY_LOCAL_MACHINE\SOFTWARE\Ipswitch\Network Monitor\WhatsUp Engine\Database Settings\RDC Rollup Settings]
"RDC Rollup Number Of Threads"=dword:00000001
"RDC Raw Expiration Time Limit (Hours)"=dword:00000018
"RDC Hourly Expiration Time Limit (Hours)"=dword:000005a0
"RDC Daily Expiration Time Limit (Hours)"=dword:00002238

[HKEY_LOCAL_MACHINE\SOFTWARE\Ipswitch\Network Monitor\WhatsUp Engine\Database Settings\Sample Rollup Settings]
"Removal task interval (Minutes)"=dword:0000000a
"Raw Sample Expiration Time Limit (Hours)"=dword:00000018
"Hourly Sample Expiration Time Limit (Hours)"=dword:000002d0
"Daily Sample Expiration Time Limit (Hours)"=dword:00002238
"Daily State Change Expiration Time Limit (Hours)"=dword:00002238
"Maximum # records to delete"=dword:0000012c
"RDC Raw Expiration Max (Days)"=dword:0000000e
"Passive Activity Log Expiration Time Limit (Hours)"=dword:00002238

------------------------------------------------------------------------

And here is the error message:

************** Exception Text **************
System.Exception: System.Data.SqlClient.SqlException: An error has occurred while establishing a connection to the server.  When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: Shared Memory Provider, error: 40 - Could not open a connection to SQL Server)
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
   at System.Data.SqlClient.TdsParser.Connect(Boolean& useFailoverPartner, Boolean& failoverDemandDone, String host, String failoverPartner, String protocol, SqlInternalConnectionTds connHandler, Int64 timerExpire, Boolean encrypt, Boolean trustServerCert, Boolean integratedSecurity, SqlConnection owningObject, Boolean aliasLookup)
   at System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(SqlConnection owningObject, SqlConnectionString connectionOptions, String newPassword, Boolean redirectedUserInstance)
   at System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, Object providerInfo, String newPassword, SqlConnection owningObject, Boolean redirectedUserInstance)
   at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection)
   at System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnection owningConnection, DbConnectionPool pool, DbConnectionOptions options)
   at System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject)
   at System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject)
   at System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject)
   at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection)
   at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory)
   at System.Data.SqlClient.SqlConnection.Open()
   at WhatsUp.CDb._OpenConnection()
   at WhatsUp.DBHelper.GetDeviceWithSnmpCredentials()
   at WhatsUp.DeviceListPage._PopulateDeviceListView()
   at WhatsUp.DeviceListPage.DeviceListPage_SetActive(Object sender, CancelEventArgs e)
   at WhatsUp.WizardPage.OnSetActive(CancelEventArgs e)
   at WhatsUp.WizardSheet.SetActivePage(WizardPage newPage)
   at WhatsUp.WizardSheet.buttonNext_Click(Object sender, EventArgs e)
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativewindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativewindow.WndProc(Message& m)
   at System.Windows.Forms.Nativewindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

************** Loaded Assemblies **************
mscorlib
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.42 (RTM.050727-4200)
    CodeBase: file:///C:/WINDOWS/Microsoft.NET/Framework/v2.0.50727/mscorlib.dll
----------------------------------------
VoIPConfigTool
    Assembly Version: 12.0.1.900
    Win32 Version: 12.0.1.900
    CodeBase: file:///D:/Program%20Files/Ipswitch/WhatsUp/VoIPConfigTool.exe
----------------------------------------
Wizard.Net
    Assembly Version: 1.0.3089.24419
    Win32 Version: 12.0.1.900
    CodeBase: file:///D:/Program%20Files/Ipswitch/WhatsUp/Wizard.Net.DLL
----------------------------------------
System.Windows.Forms
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.42 (RTM.050727-4200)
    CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System.Windows.Forms/2.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.42 (RTM.050727-4200)
    CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System/2.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Drawing
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.42 (RTM.050727-4200)
    CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System.Drawing/2.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
Interop.CoreAspLib
    Assembly Version: 1.0.0.0
    Win32 Version: 1.0.0.0
    CodeBase: file:///D:/Program%20Files/Ipswitch/WhatsUp/Interop.CoreAspLib.DLL
----------------------------------------
CoreVoIP.NET
    Assembly Version: 12.0.1.900
    Win32 Version: 12.0.1.900
    CodeBase: file:///D:/Program%20Files/Ipswitch/WhatsUp/CoreVoIP.NET.DLL
----------------------------------------
Core.NET
    Assembly Version: 12.0.1.900
    Win32 Version: 12.0.1.900
    CodeBase: file:///D:/Program%20Files/Ipswitch/WhatsUp/Core.NET.DLL
----------------------------------------
CoreNm.NET
    Assembly Version: 12.0.1.900
    Win32 Version: 12.0.1.900
    CodeBase: file:///D:/Program%20Files/Ipswitch/WhatsUp/CoreNm.NET.DLL
----------------------------------------
CoreInterfaces.NET
    Assembly Version: 12.0.1.900
    Win32 Version: 12.0.1.900
    CodeBase: file:///D:/Program%20Files/Ipswitch/WhatsUp/CoreInterfaces.NET.DLL
----------------------------------------
System.Data
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.42 (RTM.050727-4200)
    CodeBase: file:///C:/WINDOWS/assembly/GAC_32/System.Data/2.0.0.0__b77a5c561934e089/System.Data.dll
----------------------------------------
System.Xml
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.42 (RTM.050727-4200)
    CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System.Xml/2.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
System.Configuration
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.42 (RTM.050727-4200)
    CodeBase: file:///C:/WINDOWS/assembly/GAC_MSIL/System.Configuration/2.0.0.0__b03f5f7f11d50a3a/System.Configuration.dll
----------------------------------------
System.Transactions
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.42 (RTM.050727-4200)
    CodeBase: file:///C:/WINDOWS/assembly/GAC_32/System.Transactions/2.0.0.0__b77a5c561934e089/System.Transactions.dll
----------------------------------------
System.EnterpriseServices
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.42 (RTM.050727-4200)
    CodeBase: file:///C:/WINDOWS/assembly/GAC_32/System.EnterpriseServices/2.0.0.0__b03f5f7f11d50a3a/System.EnterpriseServices.dll
----------------------------------------

Delete the "DataSource_WhatsUp" value under "HKEY_LOCAL_MACHINE\SOFTWARE\Ipswitch\Network Monitor\WhatsUp Engine\Database Settings" key in the registry and then restart the WhatsUp Polling engine service. That should fix the issue. Let me know how it goes.