We have a problem where users with Contribute access are overwriting documents in document lists. These document libraries all inherit permissions from the parent site.
If I edit the permission level and remove Edit Items permission from the Contribute permission level then certain images on the site disappear for Contribute users and they cannot open sub-sites under the parent site, and get access denied.
If I add the Edit Items permission back it reverts and users can access the sub-sites and see the missing images.
I don't understand why Edit Items, a single permission, can block access to a whole sub-site? Note that sub-sites inherit all their permissions from the parent.