SQL Database Access

I have a client using Windows XP Professional on a Dell laptop. This client recieves the following error when he attempts to access a SQL database on our Win2003 server-

Connection Error:
SQL State ‘28000’
SQL Server Error; 18456
[Microsoft][ODBC SQL Server Driver][SQL Server] Login failed for user ‘labormgmt\SAli’

However, I can log on to this client using my profile and have no trouble. I have checked permissions and the user has the exact permissions as I and has Adminstrator privileges for his local PC.

What could be the problem?