Fulfillment date is coming ahead of Requirement date

There are 2 locations in my supply chain. 1 is Local distibution center and the other is regional dist. center.

There is transportation lane maintained between 2 locations.

I have created demand at Local Dist Center and after SNP Heuristic the fulfillment ie, Purchase req date is coming ahead of demand date..

for eg.

Demand date is 25.02.2008

fulfillment date against the demand date is coming 28.02.2008

same is the case in the regional dist center.

Can any one help me out in solving the issue.