Model=bcmxcp
That driver is for the serial version but you don't have a serial port configured. You need to connect the UPS with the serial cable and specify what port it is connected to like so:
config setprop nut Device /dev/ttyS0
signal-event post-upgrade
signal-event reboot
NOTE: This would be if your UPS is attached to comm1, use ttyS1=comm2, etc.
OR If you want to try the "Experimental" USB driver (tested on the PW3501 and PW5110) you could try the USB driver specifically designed for Powerware?
config delprop nut Device
config setprop nut Model bcmxcp_usb
signal-event post-upgrade
signal-event reboot
Note: This driver does not use a specified port so if you added ttyS0 as above, you must remove it to use the USB driver thus the delprop line.