You probably got the "bad" market update that went out a couple days ago. Google has fixed this now. To get your tablet to reload the new update, go into settings/applications/manage and select "uninstall updates" on the market app. This will reset to the factory installed market app. Then the newer market version will be pushed out to you at some point again.
I have a Verizon HTC Incredible 2 and I am having this problem as well. I tried going into Settings>Applications>Manage Applications>Marketplace. I cleared the cache and uninstalled updates but the Market still will not open. I reviewed several sites and found no answers except at one hacker site, but I have no interest in "rooting" my Android. Any ideas for how to get this up and running?