Connection String doesn't work on the server, works everywhere else

I have connection strings that look like:

Data Source=mydomain.com;Initial Catalog=DB;Integrated Security=True

This works from our machines - except for when this code is run on the server. I get this message: 'Login Failed. The Login is from an untrusted domain and cannot be used with Windows Authentication'

If I change the connection string data source to local:

Data Source=.;Initial Catalog=DB;Integrated Security=True

It works fine from the server - but obviously doesn't from our other computers.

I know this may be a good question for serverfault - but thought it better here, as it may be a simple software workaround that fixe开发者_运维百科s it. We don't have a domain/active directory - just a few PC's all set with the same credentials as on the server.

I did check the firewall (turned it off on the server) with the same error.

Any ideas on how to fix this?

try using the server IP insed of server name - Data Source=x.x.x.x; also make sure the firewall is open to outside connections: http://msdn.microsoft.com/en-us/library/cc646023.aspx