How did I get this NullReferenceException error here right after the constructor?

Question

I\'ve had an asp.net website running live on our intranet for a couple of weeks now. I just got an email from my application_error emailer method with an unhandled exception

Answer 1

It is almost certainly a threading issue - see this question and its accepted answer.

Dictionary<>.Insert() will throw a NullReferenceException internally if the dictionary instance is modified from another thread during the insert operation.