IIS Error 500 - app pool culprit

I was helping a coworker today with an error trying to get a SharePoint site up and running.  We were able to provision a new web app with SharePoint Central Admin, and were able to create a site collection in that web app, but when we opened up the web app we got the ol' "Internal Server Error 500" error.

What was different with this one was there were no entries in the Windows event viewer or the ULS logs, so I thought it was an issue with IIS - the IIS log did show an entry with a code 500 0 0 23 and 500 0 0 22.  The problem was not with security as I thought, whether an invalid app pool ID, invalid permissions for the app pool account, having anonymous enabled on the site, and so on...

It turned out the problem was a setting with the app pool.  If you go into Advanced Settings for the app pool, the value for Enable 32-Bit Applications was set to True, but the default and proper setting is False, as shown below.

We changed the value back to False, recycled the app pool, and no more error 500!