Cannot update D-dock FX2 firmware

I have a D-dock bay, which works fine with my Latitdue D410 (Windows 7), but I want to update the FX2 firmware from A01 to A04. I run delldbup.exe and it detects the dock and says it has updated successfully. However, after power cycle, the firmware stays at A01. I have tried running delldbup.exe from Windows 7 and from cmd prompt, and as administrator. I have tried all combinations of power cycle that I can think of (restart, shut down and start, with and without removing power cable). Every time the programme says it has run successfully, but the firmware stays resolutely at A01.

Any ideas?