I spent hours trying to fix this and finally came to the solution. Clearing the market cache and removing your Google account must be done concurrently. If all else fails, remove your Google account, clear the cache for the market, and clear all cache and data from all applications and services that use the market icon. This is kind of like hunting a rabbit with a bazooka, but it'll git'er done.
To re-hash concisely:
Be aware: if steps 1, 2, and 3 don't work, step 4 can solve your problem ( it did for me ), but it may cause adverse effects or problems ( I'm not sure ).
1) Go to settings --> Account & Sync --> Click your Google account --> and click remove in the upper right hand corner of the screen.
2) Go to settings --> Applications --> Manage Applications --> Click the "All Applications" tab --> and then scroll until you find "Market". Choose "Clear Data".
3) Make another attempt to download or purchase an app.
If you still receive the error message:
4) Repeat steps 1 & 2 , but in addition to clearing the market cache ( which happens in step 2 ), look for any applications that seem related to the market ( there were multiple services and programs I found ) and clear the data/cache for all of them. When this step is completed, your tablet will reinitialize upon exit. You may receive a notification or error.
5) Restart your tablet, click the market, and you will be prompted to add a Google account. Sign in and accept the terms!!!
Hope this works!