Windows 10 increased security by no longer allowing "no password" or "no username" to connect to remote shares by default. Perhaps that's what's causing your problems? See here for more information: https://answers.microsoft.com/en-us/insider/forum/insider_wintp-insider_web/the-account-is-not-authorized-to-login-from-this/5aa0c61d-7e27-41ce-b1cd-1bedbe5c5ead?page=1&tm=1438537160769 And then here for MS's discussion on the topic (lots of upset people): http://answers.microsoft.com/en-us/insider/forum/insider_wintp-insider_web/error-the-account-is-not-authorized-to-login-from/ffa63cc0-92d0-4639-9e3f-4d50100c1841
This may not be what's causing your trouble at all, but it sounds like what I had to go through to get my NAS shares working again on my non-Homegroup networked PC's. I figured it was worth sharing.