UPS and PE860 - serial port

[kfx]

Hello List,

I have an UPS (comet Extreme 4500) that I want to connect to a brand new 
PE860 to its serial port.
The OS is RHEL 5.
The port is activated in the bios (serial port: com1).
There are a DRAC card and a SAS 5iR raid controller in the server.

When I launch upsd it says that there is no ups on the serial port. The 
UPS was working fine on another (old) server also with RHEL5.

Can it be a conflict with the DRAC card ? Does someone in the list 
manage to plug an UPS to the serial port of a PowerEdge or must I buy a 
serial to USB adapter ?

Thanks,

kfx.