Your ViewSonic monitor must be set to the Main display. To verify this please follow the steps below:  

1. Right click on your desktop and select “Display Settings”. 

2. Click on the display number at the top that you want to make the main display and check the “Make this my main display box” under Multiple displays. 

3. If the option to select “Make this my main display” is grayed out, that would mean that is the current main display.  

NOTE: Please note that ViewSplit only works on one monitor at a time.