The Filemaker user or group may be set to a limited access that would prevent editing.
The system user or group may not have write privileges on the server.
I am logging into the file in a browser via IWP with a full access user login. I am accessing it via a browser on the same machine that file resides on.
Extended Privileges on the Edit Privilege Set screen are set to "Access via Instant Web Publisning (fmiwp)" and "Access via FileMaker Network (fmapp)".
When I create a new record via IWP, the auto-fill fields do auto-fill, but any data that I enter in the browser does not get saved to the record.