TFS not showing Dev branch in target locations for merging

Question

s/w versions: TFS2008 server, VS2010, windows xp

I have the following branch structure in TFS

• $/Root/Main Branch
• $/Root/Dev/Project1

Project1 was branched off the Main Branch, few months ago. Now I need to merge the latest code in the Main Branch to the Project1 branch. During that time, some new folders were added to the Main Branch.(Main Branch/CoreDataClasses/..). So when I try to merge this new folder into the Project1 branch using the merge wizard, I don't see the Project1 branch in the list of target branches. Why is TFS not showing me my dev branch in the target branches list?