dont know if this is what your needing but here

Hi,

Look to see if some other application is using the port. The most common
cause of this problem is Windows itself. When Windows boots, it attempts to
identify (PnP) connected devices, including the posibility of a serial mouse
on Com1. If it "thinks" that it has detected a mouse, Windows assigns a
mouse driver to the port -- this means that the port CANNOT be used by any
other application!

What causes this? The way that Windows attempts to locate a mouse is by
toggling DTR and RTS during boot. It looks for serial data after this
toggle. And, unfortunately, Windows is not very smart about this. If it
sees ANY data (even data with framing, parity, or overrun errors), is still
says, "Mouse. Assign driver!" If you have some sort of device on Com1 that
spits out data at regular intervals, without a specific command, you system
will be subject to this problem.

The only real solution (the work arounds published in KB articles on the
subject simply do not work, IME), is to make sure that any device on Com1 is
disabled, or is not connected, until after Windows has finished PnP device
identification.

Dick

posted by dick on the site

http://bytes.com/forum/thread524785.html