This is not a server problem, but a problem with a modification you have installed.
Edit:
On
http://www.mknexusonline.com/forums/...ead.php?t=1325 i get a 500 error. This is not the same as the errors you previously posted. This might be caused by a malformed .htaccess file (if you have one, try to rename it and see if that solve the 500 error) or a configuration problem in your webserver.