#25 DIALSTATUS returning result as -1 and data field empty

[Debojit Kakoti]

Problem Description:

$agi->get_variable("DIALSTATUS");

return result as -1 and data field empty.

Array([code] => 200,[result] => -1,[data] =>)

and it is occasional. Most of the time it gives correct result.
Please help me to find a solution for this problem

Configuration
PHP version PHP 5.3.28 (cli)
PHPAGI version 2.20
Asterisk version 13.0.1
Operating system Red Hat 4.4.7-4