Retargeting across the 7.3/7.4 version barrier is a bit rough because of an update we made to our python scripting system.
We “fixed” this in 7.5.2, but to have it work, you also need to update your 7.3 side. Even then, the best-case scenario is that the retarget acts like a straight launch: you don’t get any passed parameters or credentials like a normal seamless retarget.
Please try this: in your 7.3 installation, back up your vision module file, and replace it with this one: [attachment=0]Vision-module.modl[/attachment]
Of course, your best bet is to upgrade the 7.3 Gateway entirely!