Yes I had this problem about 6 months ago. If you are using school Wifi for instance the Firewall prevents you from buying Drivers/CD/TD/D from the Market. This also includes selling.
Connect to a diffrent wifi or wait till you get home to do those things. I would shortlist the person just to make sure if he/she is still on the market when you are avalible to buy stuf on the market.
*Please note it is not just school that it can be blocked, work place wifi also has Wifi.
Try using a different internet connection maybe firewall is restricting transfer market.
*This was something that a person said to me about the problem 6 months ago!*