Shutdown problem

[BillP]

I'm using a UPS 1500 with Power Chute Business Edition 9.0 on WinXP SP3.

When I interrupt the main power, the USV correctly detects the power fail and I get a message on my WinXP screen.
But when the power get back after one minute the USV recognize this but after 3-5 minutes the workstation was shut down.
I try shutdown to set shutdown at 30 minutes or at "run-time remaining" - but the workstation shuts down after 3-5 minutes.
That's not what I want! (Also the same problem with version 9.0.1). The status of the battery says there ist 47 minutes remaining battery power.
The only way to get the workstation working again is to press the ON (1) button at the USV.

Here are the logged events:
- Communication established
- Shutdown process started
- Communication lost while on battery
- Power failed
- Communication established

So is there anything wrong with my UPS-hardware or do I have some misconfiguration on my Power Chute Business Edition?