Hello,
for all of those having the same problem:
This is due to the Signature Track being the first one in the list. The only known work-around is to open the project in the version it was created in, add (for example) an empty MIDI track before the Signature Track and save the project. It will open then.
[Edit: The same happens with projects created in 8.0.30 and opened in 7.5.x or 8.0.10 - the work-around is the same]
Kind regards,