After Effects takes a long time to start (or issues an error message or crashes) because the permissions for the Adobe preferences folders have been set incorrectly. After Effects may report that QuickTime is not installed or warn that it could not create a certain preferences file.
In the following location, set the entire Adobe preferences folder and its contents to read/write:
For more information, see Set permissions for items on Mac.
For more information, see Set permissions for items on Windows.