Files on ReadyNAS read only after saving

I found the "Notify me upon replies" default so I should get notifications going forward. In case it helps:

Active Directory setup involves one trusted domain: homedomain.lan is the local domain, remotedomain.local is the remote domain. Users and groups from both domains appear in the User Accounts list. No quotas are assigned (that is to say, each Quota entry is blank). No private home folder shares enabled.

CIFS settings:
Default access: Read/Write
Allow guest access: enabled
Groups allowed full control on share ACL: homedomain.lan\users, remotedomain.local\remoteusers
Recycle bin: enabled (default settings)
Advanced CIFS Permission: Automatically set permissions ... enabled, Do not allow ... disabled, Group Rights: Read/Write, Everyone Rights: Read/Write
Oplocks: enabled

Advanced Options:
Share folder owner: root (will not let me change)
Share folder group: domain users (will not let me change)
Share folder owner rights: Read/Write (greyed out, unchangeable)
Share folder group rights: Read/Write
Share folder everyone rights: Read/Write
Set ownership and permission ... disabled
Grant rename and delete ... enabled
Advanced Share Utilities: disabled

While I do not care for these security settings, this was the only combination out of dozens we tried that would actually let our local and remote domain users use this file share without multitudes of Access Denied, Parameter is Incorrect, etc., error messages.

TIA