来自Access DB的数据不会加载到文本框中

Question

我正在尝试从本地Access数据库加载一个字符串数据，当我按下按钮时，数据将无法加载，并且出现以下错误：

  

“在System.Data.dll中发生了'System.Data.OleDb.OleDbException'类型的未处理异常

     

其他信息：条件表达式中的数据类型不匹配。”

string strProvider = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\training\Documents\Visual Studio 2013\Projects\WindowsFormsApplication1\WindowsFormsApplication1\LucruCilindrii.accdb";
OleDbConnection con = new OleDbConnection(strProvider);
con.Open();
string passingValue = "SELECT NumarDeOreLucrate FROM Ore_lucru_Cilindrii WHERE DiametruSuperior = " + textBox4.Text;
OleDbCommand cmmd = new OleDbCommand(passingValue, con);
OleDbDataReader reader1 = cmmd.ExecuteReader();
while (reader1.Read())
{
    textBox1.Text = (reader1["NumarDeOreLucrate"].ToString());
}
con.Close();