NullReferenceException causing w3wp to fail. How best to investigate?

Question

We have a problem in one of our web apps whereby a null reference exception is periodically causing the worker process to fail and the app pool to recycle. This is being logged in the windows event log from IIS but it doesn’t give sufficient information regarding the method or data that cased the fault. We do, however, have all the mdmp and hdmp files and the report.wer file from the report queue folder which includes the following:

Version=1
EventType=CLR20r3
EventTime=129387858105167318
ReportType=2
Consent=1
ReportIdentifier=86459756-1985-11e0-8eaf-005056870073
Response.type=4
Sig[0].Name=Problem Signature 01
Sig[0].Value=w3wp.exe
Sig[1].Name=Problem Signature 02
Sig[1].Value=7.5.7600.16385
Sig[2].Name=Problem Signature 03
Sig[2].Value=4a5bd0eb
Sig[3].Name=Problem Signature 04
Sig[3].Value=<Our internal assembly where the crash happens>
Sig[4].Name=Problem Signature 05
Sig[4].Value=1.0.2.7
Sig[5].Name=Problem Signature 06
Sig[5].Value=4d24d4d8
Sig[6].Name=Problem Signature 07
Sig[6].Value=7e
Sig[7].Name=Problem Signature 08
Sig[7].Value=0
Sig[8].Name=Problem Signature 09
Sig[8].Value=System.NullReferenceException

We don’t see this issue on our other environment(s) used for testing, only on our production server, so I’m wondering if these files are of any use in tracking down what exactly caused the problem? Can anyone offer some tips on investigating such issues?

Thanks

Answer 1

If you're really desperate then you can reverse-engineer this watson dump back to the failing statement in your code with the hints in this answer.

By far the better approach is to write an event handler for AppDomain.CurrentDomain.UnhandledException and log or display the value of e.ExceptionObject.ToString(). Gets you the stack trace as well, invaluable in troubleshooting.