ASP.NET Worker process crashing regularly

Apps under Windows x86 are limited to 2gb/ea. You can change this by adding the /3gb flag to boot.ini, but this can cause unexpected application behavior and should be used with caution. MS officially does not support this (http://technet.microsoft.com/en-us/library/bb124810.aspx)

IIS's memory limits can be set under the Recycling tab in the relevant app pool.

How are you determining that the application is never going over 500MB? If you're using Task Manager, keep in mind that it is rarely (if ever) an accurate representation of memory usage as Windows understands it. Use Process Explorer: http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx

There are a number of other relevant questions:

• Are there errors logged in your Event Logs?
• Is it a particular line of code throwing the exceptions? If so, is this OutOfMemory exception actually an IIS problem, or a code problem?
• Are you limiting your application pools at all with the Recyling setting?
• Are there any other services running on this machine?

Most likely, IIS, ASP.NET, and all their associated baggage are running up against the 2GB limit even though Windows Task Manager doesn't show it. Setting Recycling limits or upgrading to x64 will probably make a huge difference.

The reason the app pool is being disabled is because Rapid Fail protection is on, so after a number of App Pool faults it will Stop the pool rather than restarting it.

You can disable Rapid Fail protection, but obviously that means you're still getting the error and you're just restarting the app pool every time; the best solution is to find out why it's crashing in the first place.

Unfortunately the error messages you get from IIS are not terribly useful, so to get a better idea of what is causing the crash you're going to need to run an IIS debug tool such as DebugDiag or IISState to get more information about the error.

It could be a problem with the particular code a site is running, or if its happening to multiple sites then maybe it's something more general. Running these tools should give you a better idea of what's causing it.