Sure, it's possible, if there is a problem in the filter.
Why do you think it was IIRF that caused the failure?
To be certain, check the Windows Event Log. You should see an error message indicating which module caused the failure in your application pool. This will tell you for certain whether IIRF has failed.
If it is IIRF that is the problem, You will want to use IIS logs to determine which URL caused the problem for IIRF. Or, you could turn on IIRF logging to determine the URL that caused the problem. But turning on logging, with a site
that serves 5 requests per second, will produce a fairly large logfile fairly quickly. So if you turn on logging you need to take care about the logfile size.
Once you determine the URL that caused the problem, send me the URL, along with the contents of your ini file. Post them here.
And I need to know the version of IIRF as well.