Getting Data type mismatch in criteria expression..

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C#

WinForms

hi!!

this code displays result if any one field matches with the records in d/b

but i am getting an Exception...

' Data type mismatch in criteria expression.'

DataTable dt = new DataTable();

string custname = cust_name_txt.Text.ToString();

Int32 chassi, engine;


bool result = Int32.TryParse(cust_chassi_no_txt.Text, out chassi);
bool res2 = Int32.TryParse(sales_engine_no_txt.Text, out engine);

string month = sale_month_cmb.Text;

OleDbDataAdapter da = new OleDbDataAdapter("select * from  sales WHERE [Customer Name] = '" + custname + "' OR [Chassi Number] = '" + chassi + "' OR [Engine Number] = '" + engine + "' OR  [Month of Sale] = '" + month + "' ", con);


con.Open();

da.Fill(dt);              //Data type mismatch in criteria expression. occurs here..
dataGridView1.DataSource = dt;

con.Close();

all the datatypes in D/B are proper.i am using MS Access for database..

can someone please help me with this exception...