Dell T620 cannot be suspended by UPS

Hello everybody,

We purchased a Dell PowerEdge T620 and a Dell UPS Tower 1920W HV. The server is connected to the UPS by USB cable and shut down by the UPS every evening. That works fine so far. But instead of shutting down the system, I would like to suspend it (which I think would hibernate the system). When I choose the according option in the Dell UPS Management Software -> Shutdown Parameters, it doesn't work. The system doesn't hibernate, instead I get messages from the Dell UPS Management Software stating that the USB connection to the UPS has been lost, established, lost, established and so on.

I've read that the suspend function is not supported on all systems, so that might be the problem. But still, the error messages I get are quite strange. We use Windows 2008 R2 and the version of the UPS Management Software is 01.14.0002.

Your help is highly appreciated!

Cheers