Duplicate Record insersion when application get stucked asp.net -sql - AJAX

Hi everyone,
 i'm developing a web based inventory control system using asp.net 2005 and sql server 2005 .i also have used AJAX here. when running that web application (IIS) on server 2003 core 2 duo system some time application getting stucked .i have noticed on that time application has inserted duplicated records in to data base. any one who got success from that matter please help me.
Thanks
Nishantha

Create an index on one or more of the fields that should not be duplicated and make the index "unique".

Now you will get an error if you try to create a duplicate.

In other words, solve this in the database, not in your .NET coding.