Experiencing this issue on OSX 10.8.2, Sublime Build 2217. Some more curious information:
When I initially opened the project, the file I wanted to edit was missing from the folder it was supposed to be in. In fact, all files in a particular folder were missing. Surprised, I went to the Finder to see if my files were actually missing but Finder revealed their presence where expected. Immediately after viewing in Finder, Sublime Text 2 "noticed" the existence of the files and populated the folders in the sidebar.
I tried "Reveal in Sidebar" again and the same error message comes up (even after Sublime Text 2 lists the files in the sidebar): "File not found in open folders."