I was playing around with my test instance of Team Foundation Server today, trying to create a new project, when I got error TF218027 when it tried to create the Reporting Services folder for the project.  The strange thing was, this was not my first project created on this server.

I searched the Internet for anything similar, and found a post that said Reporting Services should be run with the NETWORK SERVICE account.  Since this was a hastily put together server, I was running it with the Administrator account, so I tried switching it over.

No dice.  I got the same TF218027 error, but this time it was due to it not being able to decrypt the symmetric keys.  Apparently, it's a bad thing to change the account on the Reporting Services service.

I hastily changed the account back to Administrator and resarted the service.  Interestingly enough, this seems to have fixed the problem.