It could be your X-Cart server still supporting SSLv3 and your X-Payments server not supporting it.
Check what SSL you have enabled on your X-Cart and X-Payments servers first. And your X-Cart and/or X-Payments could be not patched to remove explisit call of SSLv3 while your server environment does not support SSLv3 already.
See
http://forum.x-cart.com/showthread.php?t=70268