If you didn't start there, check out the sticky at the top of the Coffee House forum about the new CableCARD & HD Setup Wizards
If you have an installation sheet for cable card installers, make sure you are following all the steps, and haven't skipped something.
You didn't say which cable company you have. If you are with Comcast, check out the Official Comcast CableCard Thread!
which has links to a lot of helpful information, including screenshots which show what the cable card screens should look like once your cards have been activated.
There are MANY other threads about cable card installs on the forum already -- even though the forum search is not the greatest, searching for "cable card" or "cablecard" in the Help Center and Coffee House will turn up other threads.
With my TiVoHD, my TiVo wasn't acquiring the cable map. TiVo support was super helpful, but in the end he decided the card must be bad, and I got a new card and started over.
After that, the critical step was making sure the rep at Comcast knew I was starting over with a new card, and getting the pairing information entered correctly at their end.
If there is a dedicated group for cablecard installs at your cable company, make sure you have the right people, and aren't talking to a generic support person. And don't be afraid to call TiVo's support line.
What cable company are you with? What model TiVo do you have?