Gnana,
This often occurs if the CDX has been corrupted but the DBF is perfectly fine. You should try a complete rebuild of the indexes.
>System hang up when I execute a select statement
>"select * from Invoice_service where invoiceid = 11713"
>But "Select * from invoice_service" works fine and I can see all the 3 records for the invoiceid = 11713. Any suggestions Please.