Symptoms

You are receiving an "Index Out of Range" error while debugging custom code included in your K2 solution.
 

Diagnoses

In case you are getting an error while debugging some custom code in your solution this falls out of scope for K2 support, as K2 support do not support any custom code written for K2 platform.

There are two broad possibilities for why you can get issues in debug:

1) You doing development in separate environment which miss some dependencies.
2) You doing development in your target environment which has all dependencies but there is an error in your custom code which you have to debug.
 

Resolution

Normally Visual Studio debugging tools when properly used may give you enough information to isolate the root cause of the error even without deep knowledge of specific solution you are dealing with as you can just follow code logic/steps till the specific point and figure out what exactly is missing/wrong. The solution may be as simple as reading/refreshing some element in your project (debug tools may help you to define which one or at least narrow down the possibilities), e.g. it may be necessary to re-add InfoPath form in your project or something similar to this.