You can use phpgrid_error("Error message"); on server side.
Please refer sample editing > server validation for working demo.

Hi,

when user make mistake while adding record it shows error with dml query, i want to hide this, how can i do the same?

You need to set debug = 0;

$g = new jqgrid();
$g->debug = 0;

You can also change generic error message.
$g->error_msg = "Some issues occured in this operation, Contact technical support for help";

Hi Abu,
Setting debug=0 wont it stop all errors from displaying?

It will replace all error messages (dml etc) with your provided error text.

If you wish to remove the error displaying dialog (which is not recommended)
you can edit jqgrid_dist.php and remove following:

// on error
$out .= ",'loadError': function(xhr,status, err) {
try
{
jQuery.jgrid.info_dialog(jQuery.jgrid.errors.errcap,'<div class="ui-state-error">'+ xhr.responseText +'</div>',
jQuery.jgrid.edit.bClose,{buttonalign:'right'});

}
catch(e) { alert(xhr.responseText);}
}
";

You can refer demos/ediitng/server-validation.php samle code for duplicate record check.

Thx alot,

But i want to show errors on duplicate records, how to customize?
should i add in add_client ?