Schedule lines are not generating after mrp run?

Hi sap Gurus

      I am Facing a issue in generating schedule lines for current month we have given the requirment for the 3 months schedule lines are not generating for some material for the first month requirment but schedule lines are generating for 2nd & 3rd month.

why it is happening can any body help me out to solve this

I am attaching screen shot for two mateial one having schedule line genrated & another schedule line not generating

material master setting  for both material is same . in me01 mrp filed is maintaied as 2 & validity is same

Thanks & Regards

Sandeep Kumar Praharaj