asterisk users - Feb 2014 - AMI can not receive events unless keyboard input

Hi,
This is evenily.

My one Asterisk server and event listen App was working well for several month.
Yesterday My event listen app stop work suddenly.
I telnet to AMI via localhost 5038 to check the events, and I find
Asterisk does not
push the events until I press the Enter key.
When I press Enter key, all events was displayed, then stop display
new events until I press Enter key Again.
BTW, My others Asterisk box is not the same problem.
Asterisk version: 1.8.7.0

Help please!