Ok so I had exactly the same problem and I now have it fixed an hour later. Not sure exactly what I did that fixed it but all I did is the following:
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Reset the device
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Allow my network settings to be configured automatically (I previously had them in manually and it had all worked for the last two year)
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Refresh the WD Discovery tool. The ‘Map Network Drive’ section was no longer greyed out
Thats pretty much it. Hope it helps someone.