One or more selected database objects return a schema that does not match the schema of the target class
When you drag database objects onto existing entity classes, the data returned by the database object must match the schema of the target entity class. Verify that the correct database object is selected and that the correct entity class is being targeted.
To correct this error
Click OK to dismiss the dialog box.
Select a database object that returns data that matches the schema of the target class (the class the database object is being dropped onto in the O/R Designer).