Web-to-leads form - Case Origin Error

Web-to-leads form - Case Origin Error

Hello,

Last week I generated a web-to-leads form for my website. The form was tested and worked fine. Last night and this morning I have been receiving an error whenever anyone tried to submit the form reading 'Case Origin cannot be none.' See the image below.

I have tried regenerating the code, changing the optional fields, deleting and re-imputing the code but keep getting the same error.

I would be extremely grateful for any assistance.

Thank you!