The Rosetta Stone language learning application stores some of its data in the mdm.dat file located in the application's Resources folder. Should this file become corrupted or damaged in any way, you may need to replace it with a new mdm.dat file. Simply dragging the file into the correct folder will not do the trick, however. In order to apply the new mdm.dat file, you must confirm when prompted that you wish to replace the old file with a new one.
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Click the Finder icon in the computer's dock, followed by the Applications folder icon.
Right-click the Rosetta Stone application icon and select the Show Package Contents option.
Click the Contents folder, followed by the Resources folder. Drag the new mdm.dat file from the computer's desktop, or whatever folder it is contained in, into the Resources folder.
Click the "Replace" button when prompted to overwrite the existing file. Now the new mdm.dat file will be applied to the Rosetta Stone application.