Check if the user exists
using (var dbTransaction = System.Data.Entity.Database.DefaultConnectionFactory.CreateConnection("MyCon").BeginTransaction())
// ...
finally
{
    dbTransaction.Dispose();
}



You're already using the transaction in a using statement which is shorthand for try/finally, where the finally block disposes the IDisposable. So you can remove your manual finally block completely, otherwise you're calling Dispose on the transaction twice.


  clsErrorHandling.WriteLog("ImportUsersHandler", "AddUsers", ex.Message.ToString());


ex.Message is already a string, no need to call ToString on it.