I recently upgraded my W2k3 Forest\Domain to W2K2012 with no errors. Replication is working fine between all of the DC's. I now have 2 2003 DC's and 2 2012 DC's. The FSMO roles are still on the 2003 DC's and I have not moved them over yet. Today, I noticed an old 2 way external trust that was created to another domain that we no longer use so I successfully removed the trust while on the 2003 DC that was the FSMO role holder. However, when I log into the new 2012 DC's and open AD Domains and Trusts the external trust is still there. Additionally, when I look at the properties I get the response that the 'Trusted-Domain object cannot be found for the trust to domain xxxxx'
I also cannot create a new trust while on the 2012 server since the tab is greyed out. So, it was clearly removed but for some reason the 2012 DC's still see it in some way. I am not getting any replication errors or events. I hesitate to move the FSMO roles to the new DC's until I can figure out why this is happening.