said by jaa 
:I had some problems including the Media Center guide issue, so yesterday I did a clean install of Vista on my 5-day-old Dell.
The problem I have is "Error 21" trying to update the guide. The full error message from Media Center is:
The Guide could not be downloaded for the following reason: Guide server error (Code: 21).
After the reinstall, it could retrieve the guide. So I started installing other software (Office, Adobe, etc). After each install, I would test the guide retrieval and it worked.
Today, it stopped working. No changes. I tried system restore - still would not work. I did a system restore all the way back to the clean install, and it would not work.
Searching the internet, I tried these potential fixes:
1. Delete the programdata\microsoft\eHome folder.
2. Rename programdata\microsoft\crypto\rsa\MachineKeys folder and create an empty one.
Neither worked.
I have attached the trace from programdata\microsoft\ehome\EPG\tracehelper which seems to indicate that the file is downloaded ok, but cannot be decrypted/expanded.
Any ideas? Dell support is of course no help.
To expand on that fix a little, the orginal directory should have been renamed MachineKeysold instead of deleted, then you should try running the tv/guide setup in Media Center after you did the fix above?
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