I met the same error message on Windows 8.1, the solution is easy:
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Manually create the path mentioned (just for the file 'MetadataService_Client.cer'), finally it likes "C:\Users\Public\Documents\Bang & Olufsen\BeoPlayer" (for Win8.1)
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Click the 'Submit' to login again. All done. (This time you will receive "Your information has successfully been added")
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BeoPlayer v.5.04 Registration
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Your information has successfully been added
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OK
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