My app does not load due to the extension. How to remove an extension
in the designer do a right mouse click onto the x to delete it
example:

Taifun
This URL allows you to open AI2 to the Project List, without opening any project.
http://ai2.appinventor.mit.edu/?autoload=false
From that list, you can request Exports of Projects without trying to open them.
Upload the troublesome .aia here.