Because there weren’t enough sellers to offer you the necessary shares even at auction prices.
You might find some related discussion on this exact scenario
in this other recent topic-thread on losing money by shorting the same stock.
@d_p
From this post, it appears that the various possibilities involved in shorting stocks were not apparent to you yet.
Any specific reason why you tried to short this stock without fully understanding the situation?
Were you going by someone’s recommendation?
Any other reason(s) why specifically shorted IREDA recently?