have you updated to the latest version of the firmware this was a known error in older versions of the firmware your system overview page should report something like this if you have most current fw
Miner Type AntMiner-S2
Hostname antMiner
Model GNU/Linux
Hardware Version 2.2.2.0
Kernel Version Linux 3.8.13 #1 SMP Fri Jan 17 23:04:23 CST 2014
File System Version Thu Jun 19 14:16:34 CST 2014
Cgminer Version 3.12.0
latest firmware can be found here
https://www.bitmaintech.com/support.htm?pid=00720140413044945482bs4xshkh072D