Apple Logic Pro /LogicExpress Discussion

Wondering if anyone can help. I'm using Logic Studio with a Macbook
Pro.10.4.9, with a projectmix i/o. This was also happening before I
upgraded to Studio from 7.2 using a different computer and interface.
Whenever I want to play into logic, it will record duplicate notes
with every midi event, causing cancelling.I cannot seem to get it to
stop doing this, and I think i've checked everything. Besides, this is
happening right out the box - I installed studio and it was happening
immediately, so it's nothing i have inadvertently done i don't think.
Anyone have any clues? thanks!!