re: high COM port numbers in Windows.
The actual Windows API call to open a COM port is CreateFile, and while normally you just call CreateFile passing a name like COM1 or COM3 or COM9, once you get past 9, that method doesn't work. You must prepend a special string to the name, \\.\, so that for COM29, you'd pass \\.\COM29 to create file. And of course, if you're writing this in C source, you must double your backslashes, so it becomes \\\\.\\COM29.
Don't know if that's what's in play here (sounds like NOT if you don't have the "correct" type of adapter), but since someone mentioned a problem with high com port numbers and Windows, I thought I'd pass along one piece of information. And of course, if that were the problem, whoever wrote (or maintains) the software would have to fix it, it wouldn't be an end-user fixable problem.
Finally, in my experience, once you plug something in, Windows wants to keep it at whatever COM port number it originally assigned. I don't know how to "reset" this, but probably only because I've never had to.