in Management Studio, you must be logon on instance of report server and enable the property EnableRemoteErrors to see more details that error.
follow this -> Management Studio -> in screen: Connect to Server, server type: Reporting Services -> locate the server instance in Server Name; after connected, in Object Explorer, right-click in server instance -> properties -> advanced tab -> EnableRemoteErrors set property like TRUE and restart internet browser.
after this procedure, post again the errors.