I would get with RC Scoring Pro on that. He is also a dealer and may tell you why it is doing that. The other thing, I would recommend using ethernet for connection to the decoder (if your rc scoring pro supports it). Should be the cable that came with the decoder (it is a crossover cable). The RC4 decoder box is sending more info, and the software is not setup to read the software threw the serial port or ethernet port, you will have issues. RC Scoring Pro may tell you, you need to upgrade the software to support RC4, not sure on that...
Lastly, some of the usb to serial adapters do not work correctly, and if the drivers are the newest, it may not work right. I have a serial to usb, and if I used the drivers from 2008, works flawless, but if I updated the drivers to 2012, it wouldnt work... Make sure you try all the drivers available for the adapter you have.

All of this change is a pain, but it is good to have forums like this to help each other out.