Forbidden you do not have acces to this resource

Grav version: v1.6.19
Admin v1.9.12
Theme: Helium (v5.4.32 / g5_helium)

I am updating some information in my footer in the gantry5 plugin-page, layout and then footer, and when I am saving the new information will not stick. I get a message that states - Forbidden you do not have acces to this resource.
I am thinking it is a file or folder permission setting but I cannot find it.
Where or how can I find the folder/file that lacks the permission? I know how to set it but I just do not know where to find it.
Thanks

Try the suggestions in Troubleshooting - Permissions and tell us if this is still happening. I usually find the permission fixing shell script there works for me. Good luck :)