Thread: ERROR: SET TRANSACTION ISOLATION LEVEL must be called before any query

ERROR: SET TRANSACTION ISOLATION LEVEL must be called before any query

From
"Xinlin Qian"
Date:
Our system is written by java, and connect to Postgresql with JDBC.
Sometimes, when Connection.setAutoCommit() function is executed, a SQLException is throwed, and Error message is as following:
    ERROR:  SET TRANSACTION ISOLATION LEVEL must be called before any query
 
This error often occurs when system is busy. so why?