PO from RFX

Hi,

I am working in Classic scenerio SRM 7.02, using PI.

While create a backend purchase order from Accepted RFx Reponse, the backend PO number generated and it transferred thr' PI.

I need to debug the Creation of PO and generation XML for the same..?

Where i need to put the break-point..is there any class which is used for the same??

Bcz some time the PO is not created and as well as XML is not generated for this PO in SRM system iteself.

Thanks in advance.