http://www.cnn.com/2014/03/05/world/meast/gulf-qatar-ambassadors/It looks like the reason was Qatar's support for the Muslim Brotherhood in Egypt, which Saudi Arabia at least, confirmed today by Naming the Muslim Brotherhood a terrorist group.
http://abcnews.go.com/International/wireStory/saudi-arabia-names-brotherhood-terrorist-group-22815787Joining the Muslim Brotherhood on the terrorist groups are Al-Qaeda (especially in Yemen and Iraq) the Al-Nusra Front, Hezbollah, and the Yemeni Hawthis. Penalties will range from five to thirty years in prison for those who join them or support them.
