Yamaha DTXpress/DTXplorer/DTXtreme

1st...i have a yamaha dtxpress2e.
2nd...this is an excellent site for this instrument and i read the 
postings diligently.
...
ive always used the kit for practice with cordless headphones...sounds 
great.
...
i play drums for 2 bands. last night a used the kit and plug into into 
a mixer/amp.  about ten minutew into playing, the kit just froze. i 
coud see the gauges and lcd were frozen.  i turned it off and on...it 
was back to normal. 
...i'd like to know why it froze...? what did i do or not do that 
caused this?  also, im using a double kik pedal and it cancels out. (i 
have read this in other post)
any suggestions???