Upgrade from 2.1 to 2.7 fails (no replies)

Hello,

we just tried the upgrade from 2.1 to 2.7, but only get a strange dashboard afterwards (please see attached screenshot).

We wiped out the complete webspace und re-uploaded version 2.7, but get the same result.
Deleting the browser cache on FF, Chrome, IE - still not working.

PHP Version 5.3.18 with XCache

Thanks for any tips,
Thomas