I don't have an .htaccess file for that domain. I can visit the site: www.xqpx.com but if I try to view the admin folder www.xqpx.com/adminpanel or www.xqpx.com/adminpanel/index.php for example, I get that error.
Found the answer here: http://forums.digitalpoint.com/showthread.php?t=1273404#post10935671 Had to change the permissions back to 755 from 777.
500 error means something wrong happen with ur Script or cms, check ur .htaccess if problem exist and u r using wp then pm me i can do this job.