Hello Suresh
This is a warning which the User can utilize to make a decision on what to do next, and is based on the Customers' credit limit in AR.
If the AR Co. Prof option 'Prompt if over credit limit?' is checked, then OE will give a warning if the Order just entered will put this Customer over the limit, based on their outstanding, or current AR balance.
(Of course, this calculation does not take into account any unposted invoices/credit notes in OE.)
Hope this helps.
Softrak Support