Hi, I had same issue with Linksys DMA2200 media extender. Did you try to disable access controls on the shared folders you are connecting to? That solved the problem for me. Seems like when the access controls are enabled on the shared folders, Linkstation Pro Duo expects to enter a username to access them even if using guest account to access them. The media extender connects as guest and does not handle logins. So it fails, I believe. At least that's the explanation I got from Linksys. Maybe somebody can give a better explanation or has better alternative to disabling access controls. Until then, I will live with it as I can use my media extender.
Best,
Satish