Hi Jason,
Not meaning to be flippant, but is there any chance that what you are putting out is actually 60Hz when you think its 50? and vice versa.
Not saying you are, just a possibility. Seen a lot of equipment that has slide swtiches , even comupter settings for stuff like this, where it is not immediatelly apparent when one or the other is selected and could quite easily be swtiched in a way opposite to what it should be.