GB misses some edrum beats

Hi everybody,

I have a Roland HD-3 connected via midi-usb cable into iMac, using GB.

When playing on edrum kit (even if not recording) some notes played are missing (it's not a matter of latency - sounds are perfectly in time).

It's just like if GB is missing sone notes.

Help me please.

Thanx

iMac 2012

OSX Lion 10.7.5

GB'11 ver. 6.0.4