Environment: SQL Server 2005 Standard Edition (9.0.3077) running in Windows Server 2003 Enterprise Edition SP2 SSRS is started but the following entry (Event 120) is logged in Application log: The report server cannot decrypt the symmetric key. Most likely, the service account or password has changed. To continue, run rsconfig.exe to update the report server account information.\r\n Does this mean that SSRS is actually not functional at all even though it is running? If yes, I want to stop the SSRS.

If you don't intend to use it, then it's better not to install it. More on this here - http://www.sqlservercentral.com/articles/Reporting+Services+(SSRS)/62813/

I didn't install it and there is no one knows whether it is being used or not. If that message means the SSRS is not functional at all, I can stop it and won't break anything which is working. So, I hope someone can simply tell me whether the SSRS is actually functional or not.

I didn't install it so if this is not functional at all, I can just stop it. Otherwise, I need to find out what/who is using it.