That's an error in your code. Look for an index out of range or rather, an int value that's overflowing or something like that (Note: I don't do C#, so I don't know exactly what this exception is. Though, I'd bet on the second one).

Note: don't raise issues for that kind of things, issues are used when the kata is dysfunctionning. But since already 300 users completed it in C#, the problem is more likely laying on your side. When you have troubles with a kata, ask rather for a "Question".

Cheers