500 Server Error in 1.1 - works in debug

[mailnet_uk]

I've created a task earlier today that I subsequently closed.  I then had to re-open it.

Now whenever I try and edit the task I get a "500 Internal Server Error."

If I enable debug mode, it works.  If I disable debug, it doesn't.

Any ideas how I can find out what the problem is here?

[ignacio]

In debug mode it should be printing some error in 'cache/log.php'.