Of late i am facing strange problem.. i dont know if this issue is raised earlier.. i am sorry if it is. From past 2 weeks i have noticed while iir map calculation or LC calculations if i press cancel render button.. max react strangely.. i can open close material editor, i can close VFB window, i can click on any menu which shows drop down list etc etc like normal(except saving file) but my vray progress bar doesnt stops & shows that it is still calculating. I wait long for this to stop.. some times it stops successfully in 10-12 mints but most of the times it does not stop at all. If i see status in window task manager.. i see 3dsmax is not hanged but running like normal SO at this stage if i try to kill program.. file will become corrupt and i cant open it ever ( it becomes 16 kb file)! this issue is not with any particular file or project.. I am using 3dsmax 2011 64bit and vray 2.20.03 Sometime it happens while calculation, even when i dont cancel.. i notice it is stuck when i see LC or Irr map calculation progress bar is stuck, (estimated time is increasing but no progress) i feel this happens when max is Auto saving file in between calculation but i am not sure.
Any solution? 
thanks!
but i will try disabling autosave.. i will also post screenshot next time with rendering progress window along with various drop down list open at the same time.. but i dont know if this will make any sense..