Why are foreign aeroplanes violating Indian airspace?

The chartered Boeing 767 of North American Airlines carrying 205 passengers including US Marines messed up the call sign and entered Indian air space. It was the 4th case of Indian airspace violation this year. The aircraft was on its way to Utapao in Bangkok from Fujiriah in the UAE and was compelled to land in Mumbai till the confusion was sorted out by the Air Force authorities. It seems the aircraft had clearance of the DGCA (Director General of Civil Aviation) but not of the AOR (Air Operations Routing) which is mandatory for any aeroplane that carries military personnel or equipment. Since this is the 4th incident of Indian air violation by a foreign aircraft, the Air Force is understandably worried. The three previous occasions were (i) on June 20, it was a Ukrainian-made military cargo aircraft AN-124; (ii) on August 27 this year, it was an Air France aircraft (A-343) in Punjab and (iii) in first week of September, a China-bound cargo plane of the United Arab Emirates (UAE) Air Force was forced to land in Kolkata.