InfoPath 2007 Forms using Forms Services in SharePoint 2007 - "This form cannot be opened. It is not workflow enabled."

You may find that when you try and open an InfoPath form (e.g. as the initiation form of a workflow) that it just says "This form cannot be opened. It is not workflow enabled".

If you go to Central Administration -> Applications Management -> Manage Form Templates, it will show your form with the Status of Installing on a permanent basis. This will never complete - so what can you do about it?

This is because the real error when uploading your form is hidden so the install of the form never completes. To discover the real error, click on the "Upload Form Template" button. Enter the file name of your Infopath template (xsn) file (typically located at http://myserverurl/_admin/UploadFormTemplate.aspx) and click the "Verify" button. Resolve these issues and the InfoPath form will deploy and install properly.

The issue I had was that:

1. I had created a new InfoPath form
2. I had published it but had not left the section entitled "If users access the form template from the published location by using a different path, such as a public URL or full network path, enter it below, and then click Next." section BLANK (otherwise it won't work)
3. You need to use the published version of the Form template, not the original design.