Billing document is not automatically posted to accounting

Hi experts,

I have a problem in the billing document that usually ,the moment i have saved the billing document an accounting document is generated.

To have this automatically ,the billing type -posting block is unchecked

so it supposed to be posted to accounting, but about 70 billing document has been stagnated yet to release

Dear experts please guide me what could be the problem

With regards,

Pratheep