Wait, maybe I read something wrong...
You're using this same Siemens cable (6ES5-734-1BD20) with STEP 5 as well as this "snide version of S5WIN", and it is working with "S5 WIN" and not STEP 5?
If that's the case, I recommend uninstalling STEP 5, reboot, rename the C:\STEP5\ directory to C:\STEP5OLD\, and reinstall V7.2... and install the 4 updates on the ISO image in sequence.