jimmypader, i just ran into the same problem. this is a rather recent development because when i first installed my child theme, this problem did not occur. a few months later (i think after a twentyeleven theme update but i’m not sure) and all of a sudden i notice my child theme, though it’s working, is not recognized in the dashboard and there’s an error msg saying the theme folder does not exist. and the only visible themes under appearance are twentyten and twentyeleven. i’ve spent the past hour trying to figure out what was wrong with my child theme and adding an index.php file to the child theme folder is all it took. whatever change caused this sure flew under the radar. they need to get the word out that style.css AND index.php ARE BOTH required if you’re making a child of twentyeleven.
