All my servers are in the same domain on the same network. ServerA cannot access ServerB through UNC path. However DNS resolves correctly for ServerB from ServerA. For example "ping ServerB" works as expected.
ServerB can reach ServerA through UNC path without any problem. Likewise all other servers and clients can reach ServerB through UNC path without any problem. The software firewall on ServerB is not turned on and there are no hardware firewalls getting in the way.
This makes no sense and I don't know how to troubleshoot it. Nothing shows up in the event logs of ServerA and ServerB has one event (repeatedly): Event ID: 3019, Source: MrxSmb.
ServerA is Server 2008 R2. ServerB is Server 2003 R2. I have other 2008 R2 servers that connect without any problem.