How to fix “The report server has encountered a configuration error. Logon failed for the unattended execution account.”
Recently after I have deployed some SSRS reports to a client staging environment, I got this error as below
After some Goggling and binging, I have found out the problem is that SSRS Execution Account in SSRS configuration manager is set to a normal user account , after the user change its password , it cause the problem above. After some further research, I have found out we do not need to have an Unattended Execution account specified as EnesysRSExtension adheres to SharePoint security and passes through the end user security to maintain permissions. So after I have cleared the SSRS Execution Account, it works like a charm.The unattended execution account refers to the SSRS Execution account from the SSRS Configuration manager as shown below.
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YBBEST SharePoint Pie 
thanks !, it helped me to fix an error.