I was experiencing problems with the market as well so I went to the app page of the android market itself where I saw this:
This app is incompatible with your BASE HTC HTC Desire.
If you have version 3.1.3, try uninstalling it and then accessing the market again, it should update to version 2.3.6 which seems to be working for me. Hopefully it won't auto-update to 3.1.3 again...