Data type mismatch in criteria expression

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C#

In my database there are few many tables, i want to join two of them.
one is Customer_Master and other is Collection

in Customer_Master table there are these following fields are available:
1.Cust_ID
2.Area_SL
3.Date
4.Cust_Name
5.Area_Code
6.Area_Name

in my Collection table
1.Cust_ID
2.Amount
3.ForMonth
4.ForYear

Now i have created an asp page form(here is the link http://i55.tinypic.com/dwqphk.jpg[^]) where i get an result using the above tables.


i am writing this sql query and get the above error:

if (rdbPaid.Checked)
            {
                da = new OleDbDataAdapter("select Customer_Master.Cust_ID, Customer_Master.Cust_Name, Customer_Master.Area_Code, Collection.Amount, Collection.ForMonth, Collection.ForYear From Customer_Master Inner Join Collection on Customer_Master.Cust_ID=Collection.Cust_ID where formonth='" + cmbMonth.Text + "' and area_name='" + cmbArea.Text + "'and foryear='"+cmbYear.Text+"'", con);
                dt = new DataTable();
                da.Fill(dt);
                if (dt.Rows.Count > 0)
                {
                    lblMessage.Visible = true;
                    lblCustomerCount.Visible = true;
                    lblMessage.Text = "Total Number Of Customer is";
                    for (int i = 0; i <= (dt.Rows.Count - 1)+1; i++)
                    {
                        lblCustomerCount.Text = i.ToString();
                    }
                    grdMCPD.DataSource = dt;
                    grdMCPD.Columns[0].HeaderText = "Customer ID";
                    grdMCPD.Columns[1].HeaderText = "Customer Name";
                    grdMCPD.Columns[2].HeaderText = "Area Code";
                    grdMCPD.Columns[3].HeaderText = "Ammount Paid";
                    grdMCPD.Columns[4].HeaderText = "Month";
                    grdMCPD.Columns[5].HeaderText = "Year";
                    grdMCPD.Columns[0].Width = 150;
                    grdMCPD.Columns[2].Width = 100;
                    grdMCPD.Columns[1].Width = 100;
                    grdMCPD.Columns[3].Width = 100;
                    grdMCPD.Columns[4].Width = 75;
                    grdMCPD.Columns[5].Width = 40;
                }
            }

can anyone help to get out of this problem.
Thanks in advance.