>Tracking events fired in treeview when I check a node, I see that if in MouseDown method I put a messagebox or wait window... the click is ignored.
>Now I need to change messagebox or wait window to another command that doesn't show anything to user and interrupts the process. Any idea?

I think I get it - if the user is not and administrator, you do not want the to change the check box. Maybe, in the Item check

PROCEDURE ItemCheck(loItem)
IF NOT lAdminUser
loItem.Checked=!loItemChecked && Set it back to original state
ENDIF

Maybe ondeay there will be a "When" method for this guy?:-)