Once in a blue moon a tech issue comes across my desk that stumps me. It doesn't always mean that the issue was difficult, often it's just something I never expected.
Recently a client had all of her WordPress websites go down with 500 Internal Errors. She was hosted through Hostgator so I promptly had a text chat with them to find out what the issue was. I wasn't stumped per say, as I've dealt with this issue before. In the past I've had some database issues that caused this, and also some plugins but since I wasn't very familiar with Hostgator, I figured I'd start there and boy am I glad I did!
Turns out the cause was MacMail leaving too many IMAP connections open. That in turn left too many processes running on Hostgaters side. So how did we fix it? We moved her off of MacMail and on to Thunderbird for the time being ( Tech support at Hostgator said MacMail is poorly coded, hmpf ) and we will eventually move her to Google Apps. I didn't think moving to Google Apps would be smart when this happened as we couldn't do the verification process since the entire database on our end was down.
So after removing all accounts off MacMail we called over to Hostgator and they saw the rouge processes running, removed them and we were back in business. What an easy fix! Wheeeeeeeeeeeeee!
EDIT: The site went down again as we tried Outlook ( Office for Mac ) so same thing happened. Turns out shared hosting on Hostgator is going to do this no matter what because they limit the amount of connections allowed. So you can either upgrade to VPS or Dedicated, or stay with shared and cut down your connections and use Google Apps. HMPF