There may still be some folder/files left over.
You have to be 100% sure that you removed everything, before installing a new version of Gimp. If anything is left behind it could effect any other Gimp installation.
I know nothing about your OS, so I can't tell you where to look for any such left over folders/files.
Have you ever tried CCleaner?
Maybe this program can find any stray stuff form your previous installation of Gimp.
You can download the free version of it here...
http://www.piriform.com/ccleaner/download?mac