Indicator Methods (A Scope problem?)

I'm using a library in an indicator, the class variables of the library are declared in the indicator and the instances are created in the 'initialise' section. I have a method in the indicator that does some processing, I only want to call it from the cBot e.g.

myIndicator.myMethod(index);

If the method is called from inside Calculate it works fine, however if the method is called by the cBot I get the following error:

InvalidOperationException: Operation is not valid due to the current state of the object.

Originally instantiating the class in Calculate (even though the variable is part of the indicator) caused a null ref when the method tried to access it. Now I have this error. Whats going on here and how can I make this object accessible here?