Hi thina,
Cause this issue because the operator version not match the server side livesuport version.
Two ways(only use one of them)
1. Download the latest version of operator and livesuport server site files both and deploy the server side livesupport again.
Latest version of livesupport downloads http://cutesoft.net/downloads/folders/21856/download.aspx
2. Open file "LiveSupport.exe.config", you can find it under the operator install root.
Add the coce below into the <appSettings> section
<add key="UseOldEncode" value="True" />
Regards,
Ken