This information applies to Avid Studio which runs on iOS.
At the time of this printing YouTube limits uploads to 15 minutes. Be sure your project length is under this duration.
If you have a verified account with YouTube to accommodate longer durations, Avid Studio will support your upload.
There is also a known issue in Avid Studio 1.0. If you have a new YouTube video account, either created on PC or via the iPad, the first attempt to upload may fail. If this occurs return to editing your project and make a single change. This could be a one-frame difference. Return to the YouTube share option and now the export will succeed.