I have a form library on my site (SharePoint 2010 and InfoPath 2010) and we want any user in our network to be able to submit items, but only a select group of users to be able to edit items once they're submitted.
I figured that would be easy enough, create a permission level for the "catch-all" group to be Add Items, and create an "Editors" group that has Contribute Access (Add and Edit).
The problem is that when the Add-Items users try to submit a form they get a "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" error.
Why would these users be unable to add an item to a list where they have Add Item permissions? It seems that you need to have edit permissions as well! This seems a little counter-productive to me.