Credentials used to run this report are not stored
In Reporting Services there is a feature to Cache a temporary copy of the report that can be used to paste elsewhere.
If the proper username has not been granted on Report Manager the user will get error "Credentials used to run this report are not stored". To avoid the issue on the Report Manager choose properties of the report, click on Data Sources by selecting 'Credentials Stored security in the Report Server', enter valid user name and password that has relevant privileges on the server with atleast Power User rights.
Rest is your...