Add Max Pool Size in your connection string
ex:-
<add name="entityConnection" connectionstring="metadata=res://*/EntityDB.csdl|res://*/EntityDB.ssdl|res://*/EntityDB.msl;provider=System.Data.SqlClient;provider connection string="Data Source=ServerName;Initial Catalog=DB_Name;Persist Security Info=True;User ID=sa;Password=password;<b>Max Pool Size=500</b>; MultipleActiveResultSets=True"" providername="System.Data.EntityClient" />