Q:

an unhandled win32 exception occurred in w3wp.exe

I get the following exception when trying to load an ASP.NET MVC website:

Unhandled exception at 0x07070a91 in w3wp.exe: 0xC0000005: Access
  violation reading location 0x00000000.

The Visual Studio Just-In-Time Debugger opens and the only information I can see in the debugger is this:

Call stack location:
msvbvm60.dll!06c00a91()

The website uses some COM objects and everything worked fine until last week. This problem appeared out of the blue.
This is the error log from Windows Event Viewer:

Faulting application name: w3wp.exe, version: 7.5.7601.17514, time stamp: 0x4ce7a5f8
  Faulting module name: MSVBVM60.DLL, version: 6.0.98.15, time stamp: 0x4a5bda6c
  Exception code: 0xc0000005
  Fault offset: 0x00030a91
  Faulting process id: 0x1a0
  Faulting application start time: 0x01cd31fcb47f66d8
  Faulting application path: C:\Windows\SysWOW64\inetsrv\w3wp.exe
  Faulting module path: C:\Windows\system32\MSVBVM60.DLL
  Report Id: f5db0ae3-9def-11e1-ad79-005056c00008  

Do you have any suggestions to help troubleshoot this problem?
Edit: I managed to solve the problem and now everything works. The solution involved tweaking some registry settings that the custom dlls need in order to function properly. So the problem didn't actually appear out of the blue, I just didn't realize some registry values were modified, which caused a com dll to crash.

A:

Open the Advanced settings dialog of the Application pool that is serving the application in IIS Manager, and set: Enable 32-Bit Applications to True

A:

The information you provided above is not enough to provide a root cause however if you can provide more info about the exception you might get exact reason for this failure. You asked for suggestion to troubleshoot this problem so here they are:
You can use either any one of the 3 tools to troubleshoot this issue:

IIS Debug Diagnostics Tool v1.2
Here is more info about how to use this tool:
 http://support.microsoft.com/kb/919790
DebugDiag
Use the link below to understand how you can hook your w3wp process (it is user mode proces) with DebugDiag and collect more info about the crash:
http://msdn.microsoft.com/en-us/library/ff420662.aspx
WinDBG
Here is a link which will help you to load W3WP process in WinDBG and use some commands to extract more info about the crash:
http://blog.whitesites.com/Debugging-Faulting-Application-w3wp-exe-Crashes__634424707278896484_blog.htm

Once you have more info about the exception, you can add above and will get prompt help.

A:

Do the Following,
1) Give full rights to Temp & %temp% folders
2) Go to application pool properties & Change " Enable 32 bit application " to true

