CF 10 errors show Error 500 instead of normal error message

Hi,

Strangely, our CF 10 server has started to show "500 - Internal server error" whenever a CF error occurs, instead of the normal error message. The error is logged, but the front end shows the error 500 and nothing else. Normally, we'd see the error message and stack trace etc.

How would I troubleshoot that?

EDIT: This is a CF10 on IIS 8 Windows 2012 server, with update 11.

Regards,

Mark

Message was edited by: tribule