I am struggling too. I have always used the 'generic perspective' to navigate the 3D environment since I purchased version 11 in 06. On this particular occasion, when I switched from the Design Development First Floor Plan, to the 'generic perspective', it switched but would not allow any operations. Neither orbit, fit screen or zoom in or out worked and still doesn't. I have not yet opened other past files to see if this will occur with those files but I assure you this is real and is problematic for my latest file. I don't mind reloading 16 but might have to spend the time to update but that's ok if that is the fix.
Thanks for responding,