Adding to a generic dictionary causes IndexOutOfRangeException

Question

I\'m using a dictionary inside of some Task.

Logically I have set it up so that my Keys will never clash, though sometimes when I am adding to the dictionary I get this

Answer 1

So you might think Whatever! it will just break the one time - but nope:

Important: Once the dictionary is broken it is broken!

There goes three hours of sales (until IIS recycled on a schedule) because of a dictionary added for debugging purposes that wasn't ever even being read from.

Note: This was running for 3.5 years before I hit this condition.

 private Dictionary _debugLookup;

 _debugLookup[key] = virtualPath;

This wasn't even a static dictionary - it was an MVC IViewLocationCache that was an instance method.