ما الخطأ في هذا الكود

بســم الله الـرحمــن الرحيــم

sql = "select employe_no from table1 "

con.Open()

cmd.Connection = con

cmd.CommandType = CommandType.Text

cmd.CommandText = sql

dr = cmd.ExecuteReader

Do While dr.Read

sql = "insert into table2 (employe_no)values (,'" & dr.Item("employe_no) & "')"

cmd.Connection = con

cmd.CommandType = CommandType.Text

cmd.CommandText = sql

cmd.ExecuteNonQuery()

Loop

dr.Close()

Close_Con()

يعطي الرسالة الخاطئة التالية

There is already an open DataReader associated with this Command which must be closed first.