The Dalai Lama has cancelled his trip to South Africa, where he had been invited by fellow Nobel Peace laureate Archbishop Desmond Tutu.The Tibetan spiritual leader's office said the South African government had failed to grant him a visa on time.He was due to take part in Friday's celebrations to mark the archbishop's 80th birthday.Pretoria has maintained that it did not come under pressure from China to stop the visit.The BBC's Karen Allen in Cape Town says protests have been held outside South Africa's parliament by the Dalai Lama's supporters who say the country's sovereignty is being compromised.It is the second time in two years that the Dalai Lama's visit to South Africa has been blocked.