Odd problem with sharing across two Domains in a single Forest.
Domain controller DC1 is in Domain1. Domain controller DC2 is in Domain2. Both domains are separate trees in the same Forest. Both DC's are Windows 2008 R2.
No problem with browsing for users and groups across domains and assigning the relevant permissions to shares and folders. No evidence of replication or other AD issues.
Permissions on shares and folders are definitely correct.
We can browse to System shares across domains. Eg browse to \\dc1\sysvol or \\dc1\c$ from DC2 (or another machine on Domain2) works as expected. (Using FQDN, just shortened here for easier typing).
Browsing to \\dc1\myshare from DC2 or another machine on Domain2 brings up a "path not found" error. Actual error varies depending on OS but they are similar. Shares work as expected within Domain1.
Server1 is a member server (Windows 2008) on Domain1. No problem browshing to shares on Server1 from Domain2.
The same problem occurs in reverse - ie accessing shares on DC2 from Domain1.
We have many other domains set up in a similar way using Server 2008 DC's and have not encountered this problem. The problem seems limited to Server 2008 R2.
I have seen similar issues with SMB shares when operating across WAN with IPSec VPN, but this is across a Gb switch. Servers are on seperate subnets but there is no network security between them. FIrewall on the Windows servers has been disabled.