Symptoms

I am encountering a problem when trying to lookup a Serial Number in the Activity Instance Destination Smartobject. I'm passing in some variables to filter the results and it is not returning anything when the rule is fired in the Form. However, it works just fine when testing the exact same variables in the SmartObject Service Tester.
 

Diagnoses

As the "Activity Instance Destination" is a reporting Smartobject it could be that in the Smartobject Service Tester tool, it is executing as a different user than during Smartforms Runtime reporting Smartobject are affected by process level > Admin/View/View Participate rights.

Smartobject Logging can be enabled to determine if there are any differences in the BrokerPackageIn/ServicePackageIn/Authenticating user when executing via the Smartobject Service Tester tool vs Smartforms Runtime:

http://help.k2.com/kb000298
 

Resolution 

User was testing with different accounts.  Use the same account or perhaps grant process rights to the relevant users.