This is an issue with the MSCOMM.OCX (microsoft) which is used to access the serial ports.
Here is a discussion and 'hack' to increase the number of ports to 99. I've tested it, it works, but if you try it and things go wrong I accept no responsibility. Sorry!
You need to use a hex editor to change the sequence in MSCOMM OCX of:
3D 10 00
to
3D 63 00
It also lists a hex editor to use:
http://www.febooti.com/products/filetweak/members/hex-editor/
Once installed, when you open the properties of the file, there will be a HEX editor tab. I've tested on XP, hope it works on Vista.
After that's done, you can modify simply type in the higher port number and the software should accept it.
Let me know if this works if you try it.
-Martin