In a Public Contact Folder, there a number of users individually listed with either "reviewer" or "owner" permissions. For some reason, one of the users listed as "Owner" can not edit existing contacts. She can change permissions. She can add a contact. She can edit a contact she adds. But she can not edit existing contacts. The exact error message is:
"Your changes could not be saved because you don't have permission to modify some or all of the items in this folder. Do you want to save a copy of this item in the default for for the item?"

One other note - this folder is using a custom form.

I have check groups and permissions and can not see anything wrong.

Any ideas?