Server Application Unavailable

Hello

I got a client who uses what appears to be ASP.NET 2.0. I come from a UNIX/PHP/Apache background, and I'm not too familiar with ASP.NET. He had some permissions problem a few weeks ago that I managed to fix. Now, he's getting this error (similar to the one a few weeks ago):

Server Application Unavailable
The web application you are attempting to access on this web
server is currently unavailable. Please hit the "Refresh"
button in your web browser to retry your request.

Administrator Note: An error message detailing the cause of this
specific request failure can be found in the application event
log of the web server. Please review this log entry to discover
what caused this error to occur.

I'd actually likely be able to figure this out on my own if the administrator note were correct, but I can't find anything in the event log about the issue either. Trying to run the application over and over produces no record of a problem in the event log.

The configuration is Windows 2000, with .NET 2.0 the default ASP.NET runtime environment. He uses IIS (I'm guessing version 5, but I'm not even sure where to look).

There were some application events earlier today:

aspnet_wp.exe could not be launched because the username and/or
password supplied in the processModel section of the config file
are invalid.

I see nothing about username/password in the processModel Section of that file, which appears to be:

C:\WINNT\Microsoft.NET\Framework\v2.0.50727\CONFIG\machine.config

The process model tag seems to concist of:

<processModel autoConfig="true"/>

Another event:

aspnet_wp.exe could not be started. The error code for the
failure is 80004005. This error can be caused when the worker
process account has insufficient rights to read the .NET
Framework files. Please ensure that the .NET Framework is
correctly installed and that the ACLs on the installation
directory allow access to the configured account.

I also changed the ASP.NET state service to run on a local system account instead of some ASPNET account. I'm not even sure what the hell the ASP.NET state service does, so maybe I shouldn't even have monkeyed with it.

I'm noticing that a few versions of ASP.NET appear to be installed concurrently. 1.0, 1.1, and 2.0 as far as I can tell.

Any suggestions about to fix this would be greatly appreciated, or even URLs in the right direction.

Thank you!
.