IIS7, "HTTP Error 503. The service is unavailable", AppPoo..

my AppPools keep failing, errors in EventViewer say

Failed to find the RegisterModule entrypoint in the module DLL C:\bin
\php5\php-cgi.exe. The data is the error.

This was a module I created at one time, but I later removed it. I
have check my modules both at the machine level, the web site level,
and the application/folder level and there are no references to this
anywhere.

I searched the registry and all files in c:\windows and found nothing

I don't know what is referencing this and how to find it so I can't
get rid of it. My IIS is completely useless. I've uninstalled and
reinstalled IIS but when I reinstalled all of my metadata settings
reappeared, I wanted a clean install of IIS.

The whole reason I did this is because a PHP app that was running fine
for some time now stopped being able to load a PHP module, then the
whole PHP app wouldn't work at all. I tried all kinds of ISAPI/Module/
Script map settings, including trying to use the php-cgi.exe instead
of the ISAPI DLL. Now my entire IIS is hozed and my .NET apps don't
work anymore. I'm about ready to throw this computer out the window
if I can't figure out how to get my app pools working again. I don't
know why what was once working no longer works. The only thing I can
think of is a Windows update that changed something in IIS.

Now I don't care about getting my PHP app running IIS again, I'll use
Apache if I have to. But I need my .NET apps that I develop to work
and I can't get those working now either.

I'm on Vista Ultimate, 32-bit.

David,

Thanks for all of your help. It is very informational. Luckily,
about 6 hrs after I wrote that post I noticed that Vista had created a
Restore Point for me last Saturday when I did a backup (using the
built-in Vista backup software) so I restored the OS from that restore
point and everything was working as before. Whew! Thanks Vista!