Thanks for your replies.
I had specified output frequency based on "evenly spaced time intervals" and set 50 as number of intervals. This setting resulted in nothing written on odb file.
I found out when I change the output frequency to "every x units of time" and set x as 50*stable time increment, results are written on .odb file.
Sounds my problem is solved, but I am wondering why such weird thing is happening!Appreciate any thoughts.