Our development team has found a possible root cause and workaround for error code 20 that may appear when trying to download television guide data in Media Center 2005.  The guide download error code article I previously published describes error code 20 as a file validation error, possibly caused by a mismatched guide package.  Previously, the only recommended workaround was to try downloading guide data again later.

We got a hold of a machine that was displaying error code 20, and the developer debugged and found the failure resulted from a call to a cryptographic API that is used to decode guide data (which is downloaded in an encrypted format).  For some reason we don't fully understand yet, this API returns a set of permissions that don't permit the guide data file to be opened correctly.

This workaround that we used to resolve this issue is the following:

1. Log onto the computer as a user with Administrator privileges
2. Close Media Center
3. Navigate to the %ALLUSERSPROFILE%\Application Data\Microsoft\Crypto\RSA\MachineKeys folder
4. Delete the file that starts with 1c93d682e65b0f3af0cd51385becba5e_
5. Restart Media Center and try to download television guide data again

Error code 20 is being caused by one of the machine keys in that folder, but it appears to be a different key on each computer that hits this problem.

<update date="6/22/2006"> Updated this workaround so that it only includes deleting Media Center-specific RSA keys.  The previous workaround ended up deleting the entire RSA key store, which can impact other products on the system. </update>