Simple 3 line applescript - Error -128

I have a scenario where I'd like 2 separate applescripts.

The idea is super simple. 2 Applications, but only one runs at a time.

Example: Close application 1, launch application 2 (and vise versa)

Here are the 2 scripts I have:

A.) OpenSteam

tell application "Plex Home Theater" to quit
delay 5
tell application "Steam" to activate

B.) OpenPlex:

tell application "Steam" to quit
delay 5
tell application "Plex Home Theater" to activate

The script "OpenSteam" works perfectly fine. It does exactly what I want it to do. However, the same script in reverse (OpenPlex) does not seem to work.

Steam closes, but my script then gives me the following error *Note, Plex is not launched:

error "Steam got an error: User canceled." number -128

I have no idea what this means, and was hoping someone could help me out.

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I got my initial information from here: http://ift.tt/1AewhC3 I have revised the example scripts to fit my needs.