Symptoms

SmartObject based off a web service is returning "Object reference not set to an instance of an object". This error only occurs with the SmartObject after it has been deployed to QA environment. Error is not shown with SmartObject on Dev. The SmO on Dev and QA both point to the same web service, there is not a separate one for the different environments.
 

Diagnoses

The error occurred when executing the smart object from the SMO Tester, not just when running it from a form or view.

Troubleshooting done includes redeploying package, refreshing the Endpoints Webservice in the SMO tester, restarted the Blackpearl service on the app server, did an IISReset on the web server, created a new service instance and Smart object in the SMO tester that points to the same webservice.
 

Resolution

Restarting the Server machine resolved the issue on QA and it now functions as intended.