My personal take on this is that the CableCards are not properly paired. I think the wrong numbers got typed into Comcast's computer system, and if even a single digit is wrong, it won't work.
A "re-hit" won't help with bad pairing, since it isn't changing the numbers in the system. The "hit" is just having the cable system send the authorization down right now, instead of waiting until the next scheduled time for the authorization to be sent, and if the pairing is wrong, the authorization won't work.
First, I would verify what you have: Make sure you know for certain which CableCard is plugged into which tuner (pull the CableCards one at a time, and look at the web page for the tuners to verify which tuner you yanked the CableCard from). Write down all of the numbers - the CableCard serial numbers, with the tuner numbers, with the host id and whatever-the-other-id is.
Then I would see if you can get the Comcast operator to read back the numbers from their pairing information in their computer. Carefully check the numbers they read to you, against what you wrote down. If you identify any errors, have them correct them.
(Don't read the numbers to the operator - you don't know if the operator is checking them properly. Have the operator read the numbers to you, so YOU can check them.)
There is no built-in checksum function to catch the operator if they type a bad number into the pairing system - it's not like the credit card system where there are check digits. A bad number just sits there and prevents it from working, with no other feedback.
--Don