Passenger jet forced to divert because of 'extremely pungent' smell coming from toilet

A plane packed with dozens of passengers was forced to divert after travellers complained about a "pungent smell" coming from one of the toilets on board.
The SpiceJet plane was flying from Bangalore to Delhi in India when the foul odour became unbearable.
Passengers noticed the smell just a few minutes into the flight and it got so bad that the pilots - who were also overcome by the odour - decided to divert to the nearest airport.
A spokesperson for the budget airline - whose tagline is "Red, Hot, Spicy" - described it as a "very foul smell".
Love it. Spicejet :O)
Any ideas what could have caused the smell ?
A system may fail any time, it was better than engine failure ..................
Brit, No need to panic, it would be similar to one when these passengers would smell while they would walk to their homes after landing ............