@todoublez
This script stores its state to project file (.RPP file), so you have to save the project for storing the script state data.
The error message shouldn't be appearing, though. (It's seems to be a misbehavior/bug in reaper):
https://forum.cockos.com/showthread.php?t=204653
I'll change the docking code - there's a little bug also.
Next version will require JS_ReaScriptAPI extension (for changing the window style)
Code:
-- - Space bar: run action "Transport: Play/stop"
-- - Option to remove the titlebar
-- - New mouse handling code