I think anyone who's ever tried connecting Combro with a serial - USB adapter has had problems, I did. I had two leads and found that it was the drivers. If this is your problem then here's a link to my drivers that worked for me I hope they do for you.
A better lead to get if anyone is thinking of connecting a Combro to computer in the future is this one:
Straight forward USB - Combro connection Lead
Serial - USB Drivers