VPN users can only open excel sheet as read only

[Nutthick]

I have a shared folder containing a single excel sheet (there will be more). The sheet needs to be read only to everyone, but editable to certain users. I've set up the permissions to allow 'Everyone' to have 'Read & Execute', 'List Folder Contents' and 'Read' access and then specific users to have 'Full Control'. The permissions work perfectly for users on the LAN, but anyone going in through a VPN connection can only open it as read only. The VPN settings for the users work fine for everything else, it's just this one folder.

Has anyone come across this, or knows what I'm doing wrong?

Thanks