maybe dns problem...check out this guide from microsoft!

To resolve this issue, follow these steps:
1. Click Start, click Run, type
the following line in the Open box, and then click OK:
net start rpcss
Test to see if this resolves the issue. If the issue still occurs, continue to the next step.
2. Click Start, point to Programs, point to Accessories,and then click Command Prompt.
3. At the command prompt, type ping servername, where servername is the
server, NetBIOS, DNS, or GUID name that you want to test for connectivity.

If there is a connection issue with one of these computers, contact your network administrator to resolve the issue. If the issue still occurs, continue to the next step.

4. Use the Netdiag tool that is included in the Microsoft Windows Support
Tools (included on the Windows CD-ROMs) to determine if the domain controller
is working correctly. You can perform a network trace using the MSRPC, DNS,
NBT, LDAP, or TCP protocols.

If there is an issue with the domain controller, contact your network administrator to resolve the issue. If the issue still occurs, continue to the next step.

5. Use the Netdom tool that is included in the Windows Support Tools to verify network trust relationships and reset or establish a connection to a server