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I just upgraded from v3.1.0.4 to v3.1.1. Once I did that and cleared my cache the guest-bg.jpg image no longer appears on my home page. I just get a blank "hero area":
Attachment Capture_2014-03-23.JPG not found
I have tried looking at the frontpage.guest file to see how the image is being called, but could find nothing wrong. I have made no other changes to the site so I'm confused on this. I did notice that how this page is resolved has changed in v3.1.1, but I don't know what the implications are in how the site renders. I haven't changed my main site template nor made any other changes.
You are using override template and that file outdated, please you make sure your override template frontpage.guest.php is taken from the newest file inside components/com_community/templates/default/