InfoPath Form displayed on anonymous site causes login prompt
Had this one pop up for a second time today so thought I would blog it this time.
Client created a public website for baseball signups. It was a simply publishing portal with anonymous enabled. He then created an InfoPath form and set it up to generate an email with the info from the form. He published this form to a form library using Forms Services and then embedded the form using a page viewer web part on a new ASPX page so people could just navigate and fill out the page.
The problem – the site would pop up an authentication box every time an anonymous person would visit the site. Even stranger if someone would get the authentication box and then enter proper credentials for the remainder of the day anonymous access worked fine. Then each morning back to the same problem. ODD.
Turns out the issue was the lockdown feature used with the publishing portal. Not everyone realizes it but when you create a site collection using the publishing portal there is a hidden feature that fires called ViewFormPagesLockdown. This feature, among other things, sets it so /_layouts directory is not available to the anonymous user. For more details see the ECM Team blog post. So we simply deactivated the feature and reset the anonymous permissions and life was good again.
One thing to pay particular attention to with this feature every time you toggle this feature on or off you need to disable and enable anonymous access for the new settings to take effect. That part can drive you bonkers.
Shane – SharePoint help