This error means that you missed setting an Output in your MAIN tab.
Please do the following steps:
1) Load your network file.
2) Click on the MAIN tab.
3) Right-click the ‘OUTPUT’ in the ‘MAIN_LOOP’ node
4) Select ‘Set as Output’.
** This will pop-up a dialog, prompting you to input an Output name. You can just use the default value, OUTPUT. Then, click Ok.
5) Click Save.
After those steps above try executing the network. Please let me know if this solves your problem.
HARK Support Team