You tried to execute a DBM command relating to user data in the SAP application which is stored in the DBM server for this database instance. However, this user data is not on the DBM server.
First, save the necessary user data (see: user_sap) and execute the command once again. Alternatively, you can enter the user name and password explicitly with the DBM command.
In the database manager GUI, use the command line dialog for entering DBM commands (see: Using Database Manager CLI).