Error Event 7888 : Sharepoint

Hi,

I setup a moss 2007 system with one web server and one SQL 2005 server. It
works fine. But in web server event viewer, MOSS report an error every
minute. Below are the error details.

Source: Office SharePoint Server
Category Office Server General
Event: 7888
A runtime exception was detected. Details follow.
Message: Windows NT user or group 'portalservername\adminaccountname' not
found. Check the name again.

Techinal Details:
System.Data.SqlClient.SqlException: Windows NT user or group
'portalservername\adminaccountname' not found. Check the name again.
at System.Data.SqlClient.SqlConnection.OnError(SqlException exception,
Boolean breakConnection)
at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException
exception, Boolean breakConnection)
at
System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject
stateObj)
at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior,
SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet
bulkCopyHandler, TdsParserStateObject stateObj)
at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds,
RunBehavior runBehavior, String resetOptionsString)
at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior
cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior
cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method,
DbAsyncResult result)
at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult
result, String methodName, Boolean sendToPipe)
at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
at Microsoft.Office.Server.Data.SqlSession.ExecuteNonQuery(SqlCommand
command)
at Microsoft.Office.Server.Data.SqlServerManager.GrantLogin(String user)
at
Microsoft.Office.Server.Administration.SharedResourceProvider.SynchronizeConfigurationDatabaseAccess(SharedComponentSecurity security)
at
Microsoft.Office.Server.Administration.SharedResourceProvider.SynchronizeAccessControl(SharedComponentSecurity sharedApplicationSecurity)
at
Microsoft.Office.Server.Administration.SharedResourceProvider.Microsoft.Office.Server.Administration.ISharedComponent.Synchronize()

Does anybody know what coule be the cause and how to resolve it.

Thanks in advance.