We have faced a little problem in here with the reporting services 2005; suddenly it starts to log errors in the event log without no good reason.

Here is the error:

Error rsReportServerDisabled : The report server cannot decrypt the symmetric key used to access sensitive or encrypted data in a report server database. You must either restore a backup key or delete all encrypted content and then restart the service

After we've made investigations about this error it appears that it's cause was the changing of the user that was running the reporting services successfully.

when you want to change the user that running the reporting services... there are some steps to do first to avoid seeing that error.


How to Change Service Accounts Using the Reporting Services Configuration Tool

Use the following steps to reconfigure the Report Server Windows service account: Start the Reporting Services Configuration tool and connect to the report server. For more information, see How to: Launch Reporting Services Configuration. On the Windows Service Identity page, specify the new account and password. Click Apply. When prompted to backup the symmetric key, type a password and file name for the symmetric key backup, and click OK. Each step in the service account update is recorded in the tasks panel at the bottom of the page. The Report Server Windows service will be stopped and restated during the account update. Errors that might occur include login failures (for example, if you mistype an account or password). In the unlikely event that the symmetric key is not restored, you can perform this step yourself clicking Restore in the Encryption Keys page. To verify that the account has been reset properly, open a report that uses stored credentials. If you cannot restore a backup copy of the key, you must delete the encrypted content. For more information, see Deleting and Re-creating Encryption Keys ,Backing Up and Restoring Encryption Keys but i don't recommend that try to run this command in the command utility:

C:\Program Files\Microsoft SQL Server\80\Tools\Binn> rsactivate -r -c"C:\Program Files\Microsoft SQL Server\MSSQL\Reporting Services\ReportServer\RSReportServer.config"

you should substitute your installation location with mine in the above command.

I hope this helps, if not and try this solution, if not and you can drop down the changing user issue; try to start the service with the previous user that used to run successfully and everything will be Ok.