Hi Tracy. Have just purchased Kia Sedona with a Goodmans cd/radio in mine does the same. I have the manual for the radio BUT only states if error 1,2 or 3 go to a shop! No mention of error 7 though.
I know this is not an answer but to let you know you are not alone and if either of us find out to post the answer.
Steve G x Blackpool, March 2011