Yamaha DTXpress/DTXplorer/DTXtreme

Hi all, purchased a DTxpress III recently and used it live for the 
first time on Saturday.  Had a problem with the occasional hit of the 
snare pad not triggering.  There was no particular pattern to this 
but was disappointed with this happening.  Has anyone else had this 
problem?  Is it possible to hit the pad too hard?  or maybe I wasn't 
striking the pad acurately enough?

Any views would be appreciated.