Sorry for such a late reply and by now most likely you solved the issue but if you haven't let me ask you, does it happen when you go to the market using a 3G connection or Wi-Fi? And one thing that might help is this go Menu>settings>Applications>Manage applications>Market>Clear data or Uninstall Updates.
Then again sorry for the late reply and I Hope that you have already resolved your problem but if not try the suggestion above.