Planned Order Start Date

Dear PP Gurus,

I ran MRP for one FG mat & I got planned order & Purchase requisitions after running MRP.

Here i have to start the production after procuring the raw materials.

My purchase requisition delivery date is on 30.03.2009 & my production should start on 30.03.2009

But in my planned order, strat date is 21.03.2009.It should be 30.03.2009.

Can any body tell why system is not considering Del date of Pur req?

Where I am Missing?

Thanks & regards,

Basavaraj.