subversion merge trunk -> branch: trunk changes not recognized

I'm in a pickle. I'm using SVN 1.5 at Beanstalk and Tortoise SVN client 1.6.11 x64 on Windows 7.

I'm developing on a branch and have been merging changes from the Trunk into my branch at least once a week. I recently noticed some things weren't working 开发者_如何学运维as trunk changes didn't make it into my branch. When I try to do a merge, Tortoise acts as though there are no changes in the trunk to merge. The Test Merge shows no files being added or updated.

I tried to merge my branch back to the trunk, but got a message saying that my branch wasn't up to date and told me to merge a range of revisions from the trunk.

I really don't want to do this by hand. How can I tell Tortoise and/or SVN that my branch is not up to date?

I still don't know what caused this to happen, but I did manage a work around. I instead did a backwards "reintegrate a branch into the trunk". This seemed to work good enough, but not perfect.