I was getting this error:
The source data for a patch file could not be located. (Patch: "bnet\Battle.net\SWF\MainUI.gfx". Output: "Battle.net\SWF\MainUI.gfx".) (CopyPatchConverter::Repack)
when I tried to install the patches
I figured out this is because the updated cache actually removes MainUI.gfx from Battle.net.MPQ and renames it authentication.gfx
SO if you are like me, and did one of the early installs where you replaced your SWF folder all you need to do is use an MPQ editer to put the authentication.gfx file back into Battle.net.MPQ and rename it MainUI.gfx
Hope that helps others who are having that same problem because it took me a while to figure out on my own, and I saw others with the same problem on other forums, but no solution anywhere.