Wait for External request document is waiting

Hi friends,

I am using one existing implemnted process model , These are steps in Model

1.Wait for External Request Document
2.Inbound validation
3.Send receipt Acknoledgement
4.Inbound map

Once i send my PIP document i am receiving Acknowlegement from trading partner so steps 1,2,3 completed after that again it goes to 1st step i.e., Wait for External request doc it at waiting state not completing

I thought this is because of join type condition In Wait step jopin type condition is complex condition is :
PIP Doc or (PIP Doc and Transition N8)

What should i do to over come this problem .

Please help me out.