How do add a new vendor in Multi-vendor Mode (with video)

[dirhim]

I am trying to enable the multivendor facility and I cannot enable another user as a Vendor. When I click the "Is a Vendor" button I get a message that the status has changed, but the Vendor? filed doesn't change.
I hope someone can help me.
There has a video which shows the problem.

http://screencast.com/t/TnzInPFV