HELP! Trying to Link to Subdomain from Wordpress

This is driving me nuts! I have my WP installed in the root directory with some additional pages in a subdomain (i.e www.morestuff.mysite.com).

I set up links to the additional pages in the control panel (WP 2.7) and they worked fine. I went ahead and installed my plug-ins, activated them, and quit for the day.

When I went back today and clicked on the links in the sidebar widget I got this:

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, webmaster@xxx.xxx.com 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 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.
Apache/2.2.11 (Unix) mod_ssl/2.2.11 OpenSSL/0.9.8i DAV/2 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635 Server at xxx.xxx.com Port 80

I deactivated the plug-ins, then removed them, tried everything and I'm still getting the errors. I was able to change one of the pages to www.xxx.xxx.com/index.html and I can access it, but none of the others.

I've wasted a day on this and I need to solve it or move on. Nothing from Hostgator yet... Why would they work and then screw up?

Thanks for any help you can give me.

Steve