I'm experiencing the same issue as the OP. I thought I'd give ARCXT a try with my BCT15X, but it will not recognize the scanner. Also, like the OP mentioned, when trying virtual control, it says it's waiting but won't connect, but it will still control the scanner. I've checked my drivers and they are the most current available. I'm using a Manhattan usb to serial converter, which uses the Prolific chip.
ARCXT is the only program that doesn't recognize the scanner. I've tried Freescan, Proscan, bcTool and bcprogtool and they all will connect and recognize the scanner without any problem.
It's no big deal that I can't get it to work, as the other programs will do anything I want with the BCT15X, but I just wanted to give the ARC program a try.
Pro-197 & PSREdit500 - Uniden BCT15X & FreeSCAN - Vertex FTL-2011 - Yaesu FT50R