Folder will not allow changes to files - Requires permission from Unix User\ReadyNAS

In one and only one folder on my NAS, I am getting this error when I try to edit files (cut, paste, copy etc).

How do I fix this? It seems like it would be a simple fix from teh ReadyNAS admin screens but the thing that looks most obvious - "Shares -> Files and Folders -> Reset Permissions" seems to have no effect.

I assume I simplyhave to change the owner of the folder and all of its files but I cannot see how to do that. (My IT degree is 20 years old by now...)

File Access Denied

You need permission to perform this action.

You require permission from Unix User\ReadyNAS to make changes to this file.