15 October 2012
Yes, you can file it as return under section 139(4) upto 31-3-2013. a return can be file upto the 2 years from the date of ending of such financial year or 1 year from the date of ending of such assessment year.
So in your case financial year ending for 2010-11 is 31-3-2011 and assessment year ending is 31-3-2012 so you can file upto 31-3-2013.