HTTP ERROR 500 when trying to log in to edit site

FINAL EDIT Feb 27:  Victor Massaro indicates that this is happening because the PHP ran out of memory trying to build the page and asked me if any unused modules are running on the site. 

I don’t know what modules are on there that we aren’t using so I need assistance in updating any of our modules to help speed up the script.

Original post: This error is happening more frequently. At the moment it’s about once every two days.

If I’m logged in to the site via CAS, when the page refreshes or I move to a different page to work, I lose my connection to the site. On Chrome I get a HTTP 500 error message. On Firefox and IE, it’s just a blank screen. I can access other Yale sites via CAS with no problem.  Also the Divinity site is still visible on browsers that aren’t logged in.

My connection will stay broken for several minutes, then suddenly return. While my connection is broken, my coworkers also experience the same error.

I reported this two weeks ago, but it was was intermittent at that time I couldn’t predict it and apparently it didn’t leave a record of an outage.

My connection to our site is currently broken and has been for about 10 minutes now, but it could pop back up by the time I finish writing this. Is there any way to investigate this outage?

Edit 1: I just tested my log in with our other drupal sites and was able to successfully log into them while I’m still blocked with a 500 error on my main Divinity site. 

Edit 2: My access is back.  The 500 error lasted about 20 minutes this time.