Report server cannot decrypt the symmetric key

Hi All, 

I am getting this error while opening all AX reports.

Error: Error while setting server report Parameters.Error message: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(rsReportServerDisabled).

I followed this Link:

After that  report server deployment settings validated.

Next when I open the report, it is asking username, and password.

I have given username and Password, but report is not opening.  

Please help me to solve this issue.