Every time I attempt to edit an existing landing page I receive an error stating I do not have sufficient privileges. I'm an admin and all permissions are selected. Very frustrated that instead of modifying I have to create new templates, and then on top of it, Marketo won't let me delete the old/defunct ones.
Can you create another Admin and see if the problem persists? Over the years I have had (very) occasional problems w/perms not being picked up if added after creation.
I am assuming this might not be the case but wanted to put it out there.
The permissions error for admin users is generally due to attempting to edit an asset that is in a shared folders your template that you are planning to edit is in a shared folder. Specifically one of the sharing destinations rather than the source folder.