For some time, YouTube imposed a 10 min. Duration limit to files being uploaded. The direct upload to YouTube function in PrE 11 still has that limit. This is because the YouTube Extended Accounts were not in place, when PrE 11 was written. It is likely that PrE 12 will allow for Extended YouTube Accounts, but no one knows yet. Unfortunately, YouTube's requirements and restrictions are a "moving target," and when changes are made after a software version has been written, a workaround will be necessary.
In the meantime, one can Publish+Share to a file on their computer, with the YouTube Preset, and then manually upload that longer Duration file, through their Extended YouTube Account. While not quite as convenient, as the direct upload, it allows for a video file, with more than 10 mins.
For more information on the Publish+Share for YouTube, see this FAQ Entry: http://forums.adobe.com/message/2759311#2759311
Hope that this helps explain why one cannot upload a longer Duration file, directly to YouTube, though one has an Extended YouTube Account.