I've encountered the same message, "This WXR file (version 1.2) may not be supported by this version of the importer. Please consider updating."
but everything was up to date.
I re-assigned the users, hit import, and it gives me a bunch of text saying that all of my files already exist (probably because I've tried this 30 times already...). So if the files exist, why aren't they publishing, and why can't I see them??
