C7-621 can't connect to USB in Step 7 v5.5

[e5frog]

Bought a USB interface, mainly because the old TS Adapter programming interface needed a COM-port and a COM<>USB adapter didn't help (as expected). 

Can't get it to work though in STEP 5.5, first it doesn't want to install "SIMATIC PC Adapter USB V2.0" that's present on the installation CD for the programmer - because V8.2 is already installed apparently. 
Selecting Siemens USB in PG/PC is no problem (S7USB) and it shows in the device manager as "SIMATIC PC Adapter USB" in "SIMATIC devices" (disappears if interface is disconnected) and "SIMATIC USB" in "SIMATIC Net" but I don't know if the interface works properly, must be some way of testing it. 

This is the error message: "288:91; With the interface configuration, communication in STEP7 is not possible."

Trying TS Adapter (Auto) seems to get the Tx/Rx flashing a bit but when pressing OK it says "11.159; The interface must be the only master on bus for the required online service.", it offers to adjust the interface but there's no master setting anywhere that I can find. 
It's just the C7-621 with the interface hooked up to MPI.


Any ideas?

[e5frog]

Seems it's missing a registry entry "Software/Siemens/SINEC/LogDevices/S7USB/CP_TYPE"
??