FEP 2010 : The report server cannot decrypt the symmetric key
When you change SQL services to use the Local System account then you start to install FEP Reporting role, you can see the following error :
The report server cannot decrypt the symmetric key that is used to access sensitive or encrypted data in a report server database. You must either restore a backup key or delete all encrypted content. (rsReportServerDisabled) Get Online Help Bad Data. (Exception from HRESULT: 0x80090005)
To solve this problem, you have to delete the Encryption Key from SQL Reporting Services Configuration Manager then restart the FEP Reporting installation again.