Linux PBE agent 9.01 lost communication with SMT1500i

[Anonymous user]

hi everybody
I've a linux server running Fedora 9 with Kernel 2.6.23.1-42 connected to an UPS SMT1500i via serial cable included in the UPS package
I've installed the PBE agent 9.0.1-606

I've attached to the same UPS a Netgear Nas via usb connection and it works well
I've tried to disconnect the usb cable to see if it can disturb, but it doesn't seem to be relevant

in the configuration I've been asked about kind of communication
the choices were 1)simple 2)smart 3)smart signaling

I've choosen the last one, smart signaling. Every works for a while, I can connect to web page of agent and see all parameters
After a while,PBE agent lost communication with UPS without any reason as you can see from the image

any experience like thaty?
the linux version on the compatibility chart are Redhat and Suse only, and Fedora shouldn't be thay much different
thanks
Marco