Sales Invoice not getting submitted

While most of my sales invoices are entered without any glitch, some sales invoices are not getting submitted. I cannot understand why. I have turned of stock checking so even when stock gets negative sales invoices do get submitted. But in some situation have problem submitting sales invoices.

Also will these issue reflect in logs? If yes, where can i see these logs.

Can you share screenshot of sales invoice,Stock Setting and Selling Setting?