Hi Lakshmi,
The most common reason for the Incomplete status of the Payment lot is at times during the processing of the payment lot, System does not get sufficient background processes and then in that scenario goes into a incomplete state.
Make sure that when you are processing the payment lot, no other back ground jobs are running,so that payment lot gets all the background processes for posting the payment lot.
Moreover, if such scenario happens, just click on the "Post" button.
Once you do that the status will change from Incomplete to "Direct Postings Stopped".
Don't worry on the status, System starts posting the items once again.
Once its completed, you will find the status as Postings made or Postings made, post processing is required.
Thanks,
Amlan