[Lukas Krueger]

I ran into the same problem and maybe yours is just like mine. I worked on a film in AE and PP at the same time and already imported one Sequence from PP into the AE Project. Then i created a comp in that AE Project and imported it back to PP. Then i couldnt drag this Comp into the timeline (Stop symbol Cursor). I guess (!!), it is some kind of security, that neither of the two programs run into recursive errors. (Means you import A in which B is already imported in which A is already imported in which is B etc…

TLDR: You have to create a new AE Project, in which your current PP Project is NOT already imported in. Then it all works fine again. I hope it helps anyone.