During the initial phase of SAPInst it will grant priviledges to the user account starting SAPInst.
In order to activate theses priviledges for your current session you have to logoff and logon (with the same user) again. SAPInst will do that for you except you negotiate SAPInst in a dialog to do so.
If you ommit this step (logoff and logon again) you will get this error.
regards
Peter