I had a problem with a plugin that had a custom DLL, which I put in the Max 5.0 directory
but my FreeFrame directory is as follows, and is the same as the one for 4.6
C:Program FilesCommon FilesFreeFrame

I’m using the 5.02 max/msp/jitter and windows XP on a PC

Ok, just to clarify one of the plugins I use had a dependency on a non-freefram dll, and I put that in the max5.0 directory, but the rest worked as normal in the directory I listed above… which is my regular freeframe directory.

You might try reinstalling… or making sure you aren’t somehow overriding the 5.0 freeframe external with another external somewhere else (max 5.0 is a little more "grabby" about considering things externals.) so make sure you don’t have a patch named "freeframe" or something.
Also might try sending the command to reinitialize the list of plugins.