Problem: Customer installed Office Web Apps, runs PSCONFIG and then sees the dreaded 500-Internal Server Error when browsing to site collections in their farm.
From past experience, I knew this must be a problem with the web.config and that it must have to do with installing Office Web Apps because everything was working fine just before doing so. And it was affecting all web applications on the farm. I did the basics, reset IIS, clear the config cache but none of that worked, although I hoped it would. After scouring the internet, asking colleagues, I was so happy to find this blog post that fixed the problem: http://amritatalreja.wordpress.com/2011/07/27/http-error-500-19-internal-server-error-after-installing-office-web-application/
Fight Comparison GSP vs BJ Penn I….after getting his butt kicked in the first round, GSP listened to his coach, modified his game, like I modified the web.config file per my online coach Amrita, and won by split decision. A win is a win.