The feature “Scale-out deployment” is not supported in this edition of Reporting Services

Step1 :Connect to SSMS

Step2: Open New query window 

Step3: run below query

Use Report server

go

Select * from Keys

Step4: List all the keys that needs to be deleted, except the NULL one. 

Note: Don't delete NULL this is current one.

Step5:  Execute below command

Delete from Keys where instalationID=<>

Step 6: Restart SSRS