Check Report in Browser show the following error:
In Plugin show this Error:
System.Data.SqlClient.SqlException: Cannot open database "MSCRM_CONFIG" requested by the login. The login failed. Login failed for user 'NT AUTHORITY\SYSTEM'. ---> Microsoft.Crm.Reporting.DataExtensionShim.Common.ReportExecutionException: Cannot open database "MSCRM_CONFIG" requested by the login. The login failed. Login failed for user 'NT AUTHORITY\SYSTEM'.
It looks like credentials mismatch. Check your reporting service, it should run on behalf of the user who has access to Dynmaics CRM instance it is supposed to work with.