We have a C# .NET application written against FW 3.5 that connects to a SQL server using Windows authentication on our local network. The systems running the app are using Windows 7 SP1 or Server 2008 R2 SP1.
To provide support to some of our clients, we sometimes have to VPN (PPTP) into THEIR network - separate DNS servers, different domain name, IP subnet completely different from ours.
Whenever we're connected to a client's VPN, we get the following exception when we launch our application: System.Data.SqlClient.SqlException: Login failed for user ''. The user is not associated with a trusted SQL Server connection.
We don't understand this. We're attempting to connect using credentials from the local domain to a SQL server on the local subnet. Why are we getting this error? What can we do to eliminate the problem?
We did some additional testing.
- Windows XP: problem does NOT occur.
- Windows Server 2003: problem does NOT occur.
- Windows Vista: problem does occur.
- Windows Server 2008: problem does occur.
- Windows 7: problem does occur.
- Windows Server 2008 R2: problem does occur.