When you click the "Install" button for the proper TestStand (TS) version, a dialog may appear asking you to start TS once first. This is because the installer look for the TestExec.ini file which is dynamically created at TS start-up.
If you have changed default config directory in TS, the installer will not run.
Work around options:
A: Copy the TestExec.ini file from you config directory into the default TS directory (Win 7,8,10: C:\ProgramData\National Instruments\TestStand 20XX\Cfg). This will mainpulate the installer to run.
B: Manually install the files. All the source files is located in the Virinco\WATS\SupportFiles directory in ProgramFiles.