solid light on xbee sheild

Hi,
I'm implementing wire-less communication through xbee to transmit data from Arduino to computer. But it happens at times that the wireless link is dropped and at such a stage the light on Arduino xbee sheild which is blinking under normal communication condition becomes solid.
Restarting Arduino board doesn't help the problem. But when I restart the remote xbee sheild and then restart the Arduino board the wireless link is restored.
Can anyone guess what may be the cause of this problem.

Regards
Maria