C# error in in script task

I lost my touch in SSIS. I use an execute task with a simple query select count(column) from table. Result single row, I set up the variable:

this is my scrip in C#:

		public void Main()
		{
			// TODO: Add your code here

            //Dts.Variables["User:Variable"].Value=Convert.ToString(Dts.Variables["User:Variable1"].Value;
            String MyVar = Dts.Variables["User:Variable1"].Value.ToString();
            MessageBox.Show ("MyVar");

			Dts.TaskResult = (int)ScriptResults.Success;
		}

but I retrieve the error above.