Billing date comes later than PGI Date

Dear Friends

For a particular customer, billing date is getting generated two days after the PGI date. But for all other customers we are getting billing date on the same date as PGI is done. This problem is occurred soon after we have started invoicing through scheduling agreement instead of sales order. But I went to sceduling agrement , header &item, billing . There billing date is depicted same as PGI and delivery date. The TOP in customer, Bitting tab is 30 days credit. In customer billing Tab page there is no entry that can make this change in PGI and Billing date.

Pls tell me how do I make Billing date and the PGI on the same date?

Thanks

Sangeeta