I'm using your Xencelabs Pen tablet and or Quick Keys, and when I assign the Alt + (any other Key), it is not working correctly.

This is a Windows-only issue and will be fixed in the next Xencelabs Driver release (the current Driver is 1.2.1-14).

If you are trying to assign a button on your Pen or Quick Keys to execute a keystroke that includes the Alt key, it will not work. 

An example of this is the Adobe PS Alt + Right Click combination. This keystroke combination will allow you to drag your nib Left or Right to increase or decrease the Brush size. Or Up and Down to increase or decrease the softness or hardness of your Brush.

[1] The lower button is selected to add the custom setting.

[2] The Modifier is selected from the dropdown menu.

[2,3] This shows that both the Alt and Right Click are selected. 

The issue is that only the Alt is being sent to the application. 

This shows the same setup on the Quick Keys. 

[4] The modifier Alt + Right Click is set up on button 8. When button 8 is pressed, only the Alt command will be issued.