Domain user can't save to folder

Hi,

I have a domain user who can't save to a folder. Under properties > security, they're explicitly defined as having full control. Also the group they belong to has modify access. Under advanced > effective access > they have full access and everything ticked. I'm pretty noob to file permissions, so any suggestions appreciated! :)

Also on the file server, logged in as domain admin, I can't save any files in this folder either? I can create subfolders however, but not create files in those subfolders.

Thanks