How to recall the "Create Customer Order" form customized retail form?

Question

I am trying to recall the Create Customer Order FORM using the following line of code from my customized form:

this.Application.RunOperation(PosisOperations.ConvertCustomerOrder, null);

But it is giving me following error:

Object reference not set to an instance of an object.: System.NullReferenceException: Object reference not set to an instance of an object.

Any clue? As i am passing the posTransaction object from blank operation to my customized form and even tried by writing the code like this:

this.Application.RunOperation(PosisOperations.ConvertCustomerOrder, posTransaction);

Any help would be highly appreciated. Thanks.