Bottle Import of .tar.gz wont work - greyed out

[nullopsi]

Hey folks,
I used Whisky in the Sonoma Beta and everything worked excellent. I exported the bottle and now want to import it into Whisky (Sonoma Release) but I can't select the file. It is greyed out as if not a supported format.
I created a new bottle to test, exported it as archive and it's the same with it.
Any ideas?