Yamaha DTXpress/DTXplorer/DTXtreme

I'm trying to use my DTXpress as a midi controller in cubase sx to 
control a VST. When I turn on the DTXpress and hit a pad I can hear the 
VST play 2 times then nothing. (so I hit it a couple of times and I 
only hear the vst's first 2 triggers.) The same if I play a roll. I can 
play for as long as I want, as long as I don't pause more than +/- 1 
sec..
If I press the start/s button on the DTXpress it will play a song via 
the midi cable (all instuments over the same vst (if the instrument was 
a trumpet in the DTXpress it's the vst in cubase, pretty experimental 
drumming but atleast the midi works). If I start stop the start/s 
button I will play however many times I push it, so the midi works fine.
The audio output works aswell.
So which one of you whizzkids can help me???