Is Mos Def Banned From The United States?

I saw this and it made no sense to me: Mos Def cancels a tour in the United States over immigration issues.

We regret to inform you that due to immigration/legal issues Yasiin Bey is unable to enter back into the United States and his upcoming U.S. tour has been canceled, including May 15th, Together Boston’s show at The Wilbur Theatre.

I thought Mos Def was from Brooklyn. What immigration issues could he have in the United States? This sounds like more will come from this and it will probably be crazy. Bring Mos Def back to the U.S.