No its not what i was suspecting then, a latency issue with the USB serial com port. though in saying that does the first item in the list tally up with the markings on the modem? It has been known for the port to be "software bridged" to USB and therefore in use(only one serial device can communicate on a com line at any one time), have you anything plugged to com 1 when the modem fails to connect?
The bluetooth dialup client connection is interesting, wonder if there is conflict there?