NGP cells can easily be removed from the plate if you drop it or hit it too hard.  Before you remove the media to trypsinize, are the cells adherent?  Are you applying any washing buffer before you trypsinize?  Make sure it is not directly to the cells.  You may also be over culturing the cells.  If they are over confluent, they are much more likely to detach while you are washing or removing media.

Dear Dr.Nathan,

Thank you for your reply..

 Before you remove the media to trypsinize, are the cells adherent? YES

Are you applying any washing buffer before you trypsinize? Yes 1X PBS

ANY further suggestions..