I recently came across this issue and found the following blog to be the most clear and concise solution to the problem.
http://sharepointdipesh.tumblr.com/post/15365838063/event-6050-user-synchronization-error
This blog post goes into excellent detail about how to resolve the issue.
Be aware, if you’re not a domain admin, you’ll need to get some assistance from someone who is.
Thanks Dipesh!