"The website cannot display the page" after upgrade

I am new to Asterisk and Linux, so please be gentle with me.

I have installed PBXinaFlash on my Atom powered box, so that I can learn. Version information is:

PIAF Installed Version = under HARDWARE
FreePBX Version =
Running Asterisk Version =
Asterisk Source Version =
Dahdi Source Version = 2.6.1+2.6.1
Libpri Source Version = 1.4.12
Operating System = CentOS release 6.2 (final)

When I upgraded from Version 2.9 to 2.10, I thought that I followed all of the instructions. I first upgraded the framework, then upgraded the modules. After all of that was done, I could not get the FreePBX web pages to appear. The PIAF menu comes up just fine, but when I click on the FreePBX Administration link, all I get is HTTP Error 500, “The website cannot display the page.” I am now dead in the water, as I can’t do anything with the box. Right now, unless one of you wonderful people can help me, I am going to have to wipe it all out, and start all over again.

I really have two questions:

  1. How might I have screwed this up?

  2. How do I fix it now?