[Shahriar]

Hello,
The issue was an js error in following lines in private-message/tpls/settings.php file,

jQuery('#load-data').button('loading');
jQuery('#load-data').button('reset');

It is required to load jquery ui before bootstrap js. But your theme loaded own jquery ui at the footer which messed up things.

However, i have changed those lines ,so now it does not require button widget. So everything is fine.

Thanks.