HTTP 500 error when opening OWA

You could try changing back to the old version of ASP.net to verify.  I dont have a 2008 box in front of me, but on 2003 it was...

1) Go to IIS, select the domain.
2) Right click on domain and select properties.
3) Click on the tab ASP.NET.
4) In the field ASP.NET version, select the desired version.
5) Click on Apply to change the settings.

What is the full HTTP error?

500 - Internal server error.
There is a problem with the resource you are looking for, and it cannot be displayed.

if i try to run from IIS 7.0  i get this

Server Error in Application "DEFAULT WEB SITE"Internet Information Services 7.0

Error Summary
HTTP Error 500.0 - Internal Server Error
Calling LoadLibraryEx on ISAPI filter "C:\Program Files\Microsoft\Exchange Server\ClientAccess\owa\auth\owaauth.dll" failed Detailed Error InformationModule IIS Web Core
Notification Unknown
Handler StaticFile
Error Code 0x800700c1
Requested URL http://localhost:80/ 
Physical Path C:\inetpub\wwwroot
Logon Method Not yet determined
Logon User Not yet determined
 Most likely causes:
IIS received the request; however, an internal error occurred during the processing of the request. The root cause of this error depends on which module handles the request and what was happening in the worker process when this error occurred.
IIS was not able to access the web.config file for the Web site or application. This can occur if the NTFS permissions are set incorrectly.
IIS was not able to process configuration for the Web site or application.
The authenticated user does not have permission to use this DLL.
The request is mapped to a managed handler but the .NET Extensibility Feature is not installed.
 Things you can try:
Ensure that the NTFS permissions for the web.config file are correct and allow access to the Web server's machine account.
Check the event logs to see if any additional information was logged.
Verify the permissions for the DLL.
Install the .NET Extensibility feature if the request is mapped to a managed handler.
Create a tracing rule to track failed requests for this HTTP status code. For more information about creating a tracing rule for failed requests, click here.
 Links and More InformationThis error means that there was a problem while processing the request. The request was received by the Web server, but during processing a fatal error occurred, causing the 500 error.
View more information »

Microsoft Knowledge Base Articles:

294807

That's a little better!  ... Can you check to make sure you are using .net framework version v2.0.50727(64-bit)

You should also check your ISAPI Filters specifically the bitness to find out what it is set to run:
CSCRIPT %SYSTEMDRIVE%\Inetpub\AdminScripts\adsutil.vbs GET W3SVC/AppPools/Enable32bitAppOnWin64

i see the folder and i'm pretty sure i installed it..but like i said..i had to force it to use 32 bit so i could do 2005 reporting services.  

i followed http://support.microsoft.com/kb/894435 

hmmm ok check the bitness

Microsoft (R) Windows Script Host Version 5.7
Copyright (C) Microsoft Corporation. All rights reserved.

Enable32bitAppOnWin64           : (BOOLEAN) True

ok run this:
cscript %SystemDrive%\inetpub\AdminScripts\adsutil.vbs set w3svc/AppPools/Enable32bitAppOnWin64 1

same out put

Did you restart IIS?

yes

is there a way to undo what i had to do to get 32bit to work?  do you think that is the issue

It is an issue because of a misconfigured  64bit ISAPI DLL, now I am pretty sure that you it is the bitness, it's just a matter of which one to set it to. I know there is a MS KB doc on which one to set it to, but I am not able to remember which one..sorry

yeah that got owa working again..so i guess i won't be able to run 32bit with exchange running

yeah you have to use either 32-bit or 64-bit you just can't run both modes at the same time...hence the reason OWA stopped working on you.

that sucks...thanks for the help tho

Your welcome, I wish there was a better way...you could call Microsoft...