We reported an issue not allowing AdSense publishers post AdSense Video units not only once but twice, dating back to December 21st, I believe.
A Google AdSense representative, AdSensePro Ashley, posted that the issue is now resolved. She said:
Thanks for your patience while our engineers worked to investigate your concern.I am pleased to let you know that this issue has now been resolved. Now, if your AdSense account is linked to your YouTube account, you can create video units by clicking on 'Video units' in your AdSense account.
Good news to those of you that want to give AdSense's Video Units another try. I have instructions on how to get started with AdSense Video units.
Forum discussion at Google Groups.
