Karmapa's foreign tour cancelled

This letter from a very eminent and respected Lama, Ven. Ringu Tulku has recently circulated:

Dear Dharma Friends,
I am sad to announce that the proposed visit of His Holiness the 17th Gyalwang Karmapa Ogyen Trinley Dorji was not approved by the Government of India. The visit was scheduled to take place from 27th May to 2nd July in nine countries of Europe. The Kagyu Office, the Administration of Gyalwang Karmapa was informed of the decision by the Tibetan Government in Exile on 3rd April 2010. The process has begun to find out why this visit was not possible and what positive conditions are needed to make the visit possible in near future. I know a huge number of followers and friends in Europe were eagerly waiting for the visit of Gyalwang Karmapa and I know that all of you are sad and disappointed. I would like to take this opportunity to thank all the organizers, volunteers and donors for working so hard to prepare for the visit in last many months. Your cooperation and support were beyond any expectations. I hope and pray together with you that the visit will happen in very near future and that all of us would be able to receive his teachings in Europe.
Ringu Tulku,
Coordinator,
Karmapa's Visit to Europe

Why has the Government of India refused the permission to the Karmapa Ogyen Trinley Dorji to tour six European countries?
Difficult question to answer.