Do you have a Procedure that is expecting to receive a value (argument) for processing, but a button click or other event is calling the Procedure without sending a value? Or, a Procedure that used to require a value that has since been modified to exclude it?
We shouldn't see this error in the latest versions of AI2 but it was an issue before:
https://groups.google.com/forum/#!topic/mitappinventortest/2pBa91dz8Sw