Error Type:The form cannot be submitted to the specified SharePoint list or document library. The SharePoint location may be read-only or you may not have permissions to access it.

I recently ran into an issue "The form cannot be submitted to the specified SharePoint list or document library. The SharePoint location may be read-only or you may not have permissions to access it."

Problem source is:

There is one custom list and items are added through workflow and when anonymous user try to edit and while saving getting the error.

The root cause of that error is

Possible fixes is :

Modify the Item-Level Permission to allow all users to "Create and edit all items"-
Go to List Settings –> Advanced Settings
Change the "Item-Level Permissions" back to allow all users to "Create and edit all items" – this assumes you don't need item-level permissions on this list.