Update: my problem is resolved and I can now see the Titles&Meta tabs, with wordpress 3.5, genesis 1.9.1
The problem was solved by Jennifer Baumann from the Studiopress team, and involved increasing the memory in the php.ini file from 32MB to 96MB.
Maybe this will resolve the problem for some of you experiencing the same thing as well?
PS - Thank you so much for all your help, Jennifer!!!