problem play track instrument

[LEAR]

Hi,

I have a rare problem, which must surely be a matter of configuration.
I think a channel instrument in protools 9 / mac.
I assign a virtual instrument. I play and listen to perfect.
I record the melody in the track. The midi notes are perfect record
When you play back the recording, I cut the notes. That is, the sound cut out as if it starts to ring and cut.
The strange thing I do with any virtual instrument.

Any help? Thanks for your time.
. leandro