Sorry for your issue. I see that you are not able to launch After Effects.
Could you check if you have Deep Freeze installed on your computer? If yes, remove it temporarily and check if it helps. Try giving Full Disk Access to After Effects and check if it brings any change. Here's how: https://macpaw.com/how-to/full-disk-access-mojave
EsbenHe, I kept getting the same error message. I'm not sure if this has been resolved for you, but I had success by opening another, smaller AE project then importing the project I wanted to open but couldn't, into that project. Then instead of getting that same error message, it gave me this one about not being able to find a source layer. I had to "OK" through several of these messages and the project imported successfully. Then I just deleted out all the other bins and comps I didn't need.