Anonymous Access To Domain Joined ReadyNAS

Thanks Roland and StephenB for the responses. While the users are moving from domain A to domain B, they are getting a new domain user account in domain B and their old domain A user is still active. I also tried enabling anonymous access for access and file in the NAS itself but that didn't seem to change anything. 

Both of your responses got me thinking further about the situation and I came up with something that works and allows a user to access the NAS shares after using their domain B login. Once a user starts logging into their PC using their domain B credentials, using Windows Explorer, I manually mapped a drive to the ReadyNAS share specifying the path to the share and then checking the box that says, "Connect using different credentials." Once this is checked, the user can provide their credentials from domain A and the share will get successfully mapped and allow them to access the data. I also checked the box that says, "Reconnect at sign-in" so the drive should be persistent and get mapped every time they login until the transition is completed and all share data is moved to another location.

Thanks for the help guys!