Just today I ran into this issue http://drupal.org/node/371781
I had the error message plus my theme did not work at all, all I saw was an unstyled page. Replacing an umlaut ü by ü solved the problem, like I described in my comment.
As I did see the question mark in my theme description, I solved the issue by chance. But less experienced themers might get desperate not finding the reason for this behaviour.

Some string sanitizing for the description might be a good idea an not too hard to do.

Comments

eigentor’s picture

eigentor commented

Sorry, forgot to put code brackets round my ü. Escaping the character like this was the solution I found as described.

eigentor’s picture

eigentor commented
Status: Active » Closed (fixed)

Hm, checked again in another theme - could not verify this error, must be specific to my case.