What is the meaning of "System.IndexOutOfRangeException: Index was outside the bounds of the array"?

homerm 80

I would like to know more about the "System.IndexOutOfRangeException: Index was outside the bounds of the array at System.Collections.Generic.HashSet`1."

What could cause this exception during my login and recycling the application pool in IIS resolves the exception message. Is it a runtime threading issue?

Thank you!

Yurong Dai-MSFT 2,781 Reputation points Microsoft Vendor

2024-03-19T05:27:44.98+00:00

Hi @Homer Macalintal,

The System.IndexOutOfRangeException is a common exception in .NET applications that occurs when you attempt to access an element of an array, list, or collection using an index that is outside the bounds of the data structure.
What does this mean "What could cause this exception during my login and recycling the application pool in IIS resolves the exception message"? Did you resolve the System.IndexOutOfRangeException by recycling the application pool in IIS?
homerm 80 Reputation points

2024-03-19T05:59:17.09+00:00

@Yurong Dai-MSFT Yes. By recycling the application pool can now access the application and it resolves the issue. Thank you for your answer. I know have an idea in regards to the error.
Lex Li (Microsoft) 4,742 Reputation points Microsoft Employee

2024-03-19T15:27:39.3266667+00:00

The appearance of HashSet in the exception message isn't a good sign, as such types are not thread safe and can throw exceptions like this if used in a multithreading application like ASP.NET. Can you engage the web app developers to review their code? That might prevent such from happening again.