On Fri, Sep 18, 2009 at 06:29:15PM -0700, Markus Lampert wrote:
> 
> Once the port was opened an entry is created but not destroyed on close. So when primClosePort is called by SerialPort>>openPort: an entry is found in previousSerialFiles and the vm actually tries to close that one (again). Which fails in line 186:
>  ...

Ian has apparently added your fix now:

  http://lists.squeakfoundation.org/pipermail/vm-dev/2009-September/003216.html

So I think that the problem should now be resolved in future builds.

Dave