Wordpress Plug-in Update issues

When doing a routine plug-in update on my Wordpress panel, after getting a few 404 errors, it finally gives me a "Briefly unavailable for scheduled maintenance. Check back in a minute." error that hangs for several minutes, and after that is over, my plug-ins are still not updated. HELP! The site is: http://madfitnesscenter.com

UPDATE: I tried updating individually and this seems to work. STILL want to know how I can eliminate 404 errors!