Solution
This issue is related to a software corruption, it is suggested to repair the Teststand Version Selector.
Follow these steps to do so:
1) Open
NI Package Manager2) Click in the
gear icon on the top right hand
3) Mark all the options
4) Search for the
NI TestStand Version Selector >> Select it >> Click on Repair
After this operation, NI Package Manager will ask to reboot the PC.
You should be able to open the NI TestStand Version Selector and make active the desired TestStand Version