When typing in a persons name in the recipient box, always make sure you choose the right name. Usually, if you enter in 'A' (or any other letter, etc.) before the rest of the name, you'll see the little drop down box with several members' names. If you hand slips by accident, the wrong name might be entered into the box. It's tricky sometimes, but it helps to double check. Unless the PM was directly sent to another person without you knowing it...?