File associatons...
I believe the reason there are file association problems with VE Pro is that each of the four applications (VE Pro, VE Pro 64-bit, VE Pro Server and VE Pro Server 64-bit) point to an executable file that has the same name: Vienna Ensemble Pro. So, once one program is running, trying to launch another application by double clicking on a different mframe file or a viframe file, the OS will think the application is already running because it is pointing to an executable file call Vienna Ensemble Pro and one with that name is already running. So it tries to load the file, discovers it can't since it is not compatible and either gets and invalid file error or just doesn't load the file.
Someone correct me if I'm wrong, but in OS X I don't believe you can have different programs with the same name and expect them to work consistent with the way the OS is designed.