Yamaha DTXpress/DTXplorer/DTXtreme

Hello, my name is Rolf and im a new owner of DTXpress II (1,5 month), 
and I do like it! But I've come to an end of my struggling with 
getting the midi thing working!!! I want to use DTXII with Native 
Instruments Battery and I cant figure it out, how to get it 
going!!! Everytime I start to play to play for, let say, 20 seconds, 
then a big "crack" appears and the sound goes away!!

Please help me to configure the midi, and the module right!!

The stuff I use is:
DTXpressII
Win98SE
Cubasis 4.0
I have a fast processor and nearly 1 Gig RAM so the computor shouldnt 
be the problem here.(and also newinstalled every program and drives)
I have looked in the DTXII manual plenty of time but I dont really 
seem to get it...

Thanks for your help
Rolf Antonsson