I'm not sure why you can't re-open your Ae composition.
Be sure to allow enough time for all Adobe background processes
to close before you try to re-open... better yet, reboot and try.
If you still can't open your Ae file, try importing your Ae
composition into Premiere via Dynamic Link.
File>Adobe Dynamic Link>Import After Effects Composition
If you can get the Ae comp into Premiere, you can then do
as shooternz suggests... export and re-import the digital intermediate
to Premiere for further editorial.