yes, for some reason, if you are using windows with the ArduinoBT you won't get it working if the com port is above something like 6 or 8. I taught a class with the BT last term and lots of Windows users had this problem. Can't remember what the workaround was.
Windows tends to make virtual com ports and keep them in the list, so you will have to get rid of them! Not sure how, there is probably info floating around somewhere on how to do it. There was apost on asimilar issue a while back that suggested trying this
hack to remove the unused virtual com ports.