Serial I/O with Basic Stamp

I'm trying to get a Parallax Basic Stamp to talk to Matlab over a serial port. The Stamp is connected to the same PC that Matlab is running on. If I start Matlab first and create a serial object, then when I start the Stamp I get an error "Can't open port: in use". But if I start the Stamp first, the Stamp runs fine - but then when I try to open the serial port from Matlab, it hangs on "fopen (s)", where s is my serial port object.

The Matlab code is simply

> s = serial('COM1');
> fopen (s)

and the BS code is

SEROUT  16, baudrate, ["A", 10]

This is with Matlab 6R13 in XP SP3 and a Basic Stamp 24p connected via a 9 pin serial line on COM1. There is at least one example on the web (mechatronics.poly.edu/projects/papers/BS2MatlabPaper.pdf) that claims such communication is possible, but I can't get it to work. What am I doing wrong? Any help would be greatly appreciated.