Internal Server Error while posting

I just had to switch host companies and re-install WP due to a serious error in my last blog.

I installed WP using Fantastico Deluxe and it allows me to log in and post, but as soon as I try to use any “fancy” things like the blockquote, I get this message, and cannot post anything anymore:

“Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, [email protected] and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.”

Anyone have any ideas of what might have gone wrong? I’ve uninstalled and re-installed, but get the same problem.