DIgiOne problems

Hello,

we have several « Digi One SP ».
We have some technical problems : during the FIRST use of the virtual COM port (via our software), the port isn’t accessible. Then it works everytime.
It also doesn’t work the first time we try to use it after a reboot of the computer. Then it works…

What is the problem ?
Our computer is running Windows XP pro.

Thanks you in advance.