Problems with serial port connection

Hi Folks,

since one week I´ve encountered the following problem with my windows 2003 server installed on an esxi 5 hypervisor (build 821926):

server hardware is a hp proliant dl385g5.

pbx is connected to the serial port on the server hardware (com1).

com 1 is enabled in the bios.

serial port is added to the virtual machine (settings -> serial port, connection /dev/char/serial/uart0)

Now the Problem:

I used the Virtual Server to connect my LAN to our PBX for CTI. Since one week the connection is gone. No connection between the Server an PBX is possible. PBX configuration says, that the port is in use.

This scenario works for about 10 weeks stable.

Things I´ve done so far:

-checked if pbx serial connection works (connected via laptop on serial port->works great)

-set up another windows server 2003 (on the same esxi), in thought of that the existing one is damaged or so...

-tried to reroute output for the serial port from connection /dev/char/serial/uart0 to output file. Tested with hyperterminal -> works.

I think the connection between the esxi an the hp hardware doesn´t work correctly.

Is there a way to log the traffic from the virtual serial port which is bound the hardware serial port ?

Is there a possibility that I haven´t think of...

Thanks a lot.

David