Could it be that IRServer responds to HDMI CEC information?
When I connect my HTPC to an LCD TV using a VGA cable (so analog), IRServer and USB client start normal and the USB client icon isn't flickering, indicating that it doesn't receive any commands. When I connect my HTPC to an LCD TV using a HDMI cable, the behaviour changes dramatically. The IRServer starts but puts the VFD display into a reboot cycle. The IRServer tries to hook up to the IRServer after the 20 seconds delay but fails to do so (gives me a dialog showing the version of the client with an OK button). Rebooting the complete PC doesn't solve the issue, even so, the display keeps rebooting through the complete boot cycle. Sometimes the IR client can connect without an error dialog and I can see the icon flickering continously, receiving IR commands (also visible in 'detected IR commands dialog'). Changing back to the VGA cable solves all these problems.
System is a 32bit Windows XP SP3 installation with a bare minimum of drivers and no additional PCI cards. Cabinet is a OrigenAe H6 featuring a VF110.
LCD TV is a Samsung LE26R81B connected to HDMI2 (60Hz, HDMI1 is 50Hz but shows the same issue)
IRServer 5.10.09 (from the IRTrans website)
Firmware 5.08.10 (from the OrigenAE website)
USB driver 2.02.04 (from the IRTrans website)