SQL User not found

Hi All, I have a client running Navision 3.10A with SQL Server. When I go into Navision and try Syncronise I receive the following: (Error Message 1) Click Ok if you want to revoke Windows login DOMAIN\User1 from Server SERVERNAME or click Cancel to allow login to remain granted. This message appears 4/5 times for different users, before the final error message: (Error Message 2) 15401, “42000”,[Microsoft][ODBC SQL Server Driver][SQL Server]Windows NT user or group ‘DOMAIN\User6’ not found. Check the name again. This user does exist in Active Directory! I cant add a Windows Login user either as it specifies Error Message 2. Any suggestions? [B)]

Should anyone have a similar query (error message) this article should be able to help http://support.microsoft.com/default.aspx?scid=kb;en-us;324321