Problems Modifying Keyframes in Masks.

[The Mavo]

In my After Effects project, there are some layers that include simple masks, the positions of which are animated.

The keyframes I had created to control the mask animation had been working fine. I had been able to change the layers, including their keyframes without issue. But, now, for some reason I don’t know, AE’s behavior has suddenly turned erratic and it will not allow me to modify many of the keyframes in the masks. I can’t select or move those keyframes, even though their respective layers do not appear to be locked.

And, when I try to modify the keyframes in the graphic editor (to move them or create easy in or easy out, etc.), I now receive an error mesage that reads “Attempt to get an item address from a position outside of list length. ( 27 ::15 ).” When I click OK to clear the error box, the same error automatically reappears over and over; the error will not clear.

What is happening and what can I do to modify the keyframes properly again in AE?

[Mylenium]

Without any specific info on the project, screenshots, system info and so on we can't reall tell you much. Typically such a behavior would only occur when time-remapping, nested comps with different framerates or other forms of temporal manipulation are involved like an effect referencing your mask, but we honestly can't know based on so little real info. Outside that of course the usual things apply: clear your caches, check your hardware acceleration settings, relaunch AE and reboot the system, update graphics and input device drivers if necessary.

Mylenium

[Rick Gerard]

Did you add any expressions to the masks? If you did, you have to disable the expressions before editing the mask points. 

There is also a switch to lock the Masks just to the left of the Mask name in the timeline. Make sure that is unlocked.