Merging to branch from old branch/trunk?

I'm a fairly new subversion user, so forgive me if this is some ridiculously simple problem that I should be able to figure out on my own.

I just joined a project that never branched it's project and committed everything to trunk. After convincing them to use branches, I branched the trunk code to what we will call "Branch A" and made a few changes. During this same time, some additional changes were made to the trunk code. The problem I'm having is that I'd like to merge the changes in the trunk to Branch A. But when I try to do this via subclipse, nothing happens.

I've switched to Branch A.

I do Team -> Merge

I select trunk for the "From:" and Branch A to the "To:"

I set both to Head Revision. I hit "Dry Run" or "Merge" and nothing happens. I'm clearly doing something wrong - what is it?

I've been able to merge from Branch A -> Trunk, but the other direction simply isn't happening.