Hi there-
I’ve started receiving this error in After Effects CC. If you click “ok”, to make the error message go away, it simply pops back up again. It is impossible to right click on a clip and change the frame rate. I’ve had this problem only with one clip, from a GoPro Hero 3+ Black. All other clips from the same camera don’t cause this problem, and a different section of the same clip only gave me the error once, so your method of fixing it worked. I’m at a loss.