My installation of Movable Type has been plagued with intermittent Internal Server Errors over the last few weeks. Apparently this is a known problem resulting from buggy Perl modules being automatically installed as part of a cPanel upgrade. What I have found is that entries or comments with quotes or double quotes will produce a runtime error and the resulting server error message. It should get fixed soon, but if you've tried to add a comment and received the error message, please email me at scott(a)northspace.com.
Sorry for the inconvenience.