C# 2008 object instance problem. Please help?

So I am having a bit of a problem here with a class assignment I'm doing. Yes we have to use visual studio 2008. It's a payroll system that stores the employees name, pay rate, start date, and end date into a database. Now everything executes fine until I start inputting the information. It says "NullReferenceException was unhandled by user code" with the following description: "Object reference not set to an instance of an object".

Data layer code:

// This function saves the personnel data

public static bool SavePersonnel(string Database, string FirstName, string LastName,

string PayRate, string StartDate, string EndDate)

{

bool recordSaved;

try

{

// Add your comments here

OleDbConnection conn = new OleDbConnection("PROVIDER=Microsoft.Jet.OLEDB.4.0;" +

"Data Source=" + Database);

conn.Open();

OleDbCommand command = conn.CreateCommand();

string strSQL;

// Add your comments here

strSQL = "Insert into tblPersonnel " +

"(FirstName, LastName, PayRate, StartDate, EndDate) values ('" +

FirstName + "', '" + LastName + "', " + PayRate + ", '" + StartDate +

"', '" + EndDate + "')";

// Add your comments here

command.CommandType = CommandType.Text;

command.CommandText = strSQL;

// Add your comments here

command.ExecuteNonQuery();

//closes connection

conn.Close();

recordSaved = true;

}

catch (Exception ex)

{

recordSaved = false;

}

return recordSaved;

}

Here is the frmPersonnelVerified verifying code

// saving the personnel information

if (clsDataLayer.SavePersonnel(Server.MapPath("PayrollSystem_DB.mdb"),

Session["txtFirstName"].ToString(),

Session["txtLastName"].ToString(),

Session["txtPayRate"].ToString(),

Session["txtStartDate"].ToString(),

Session["txtEndDate"].ToString()))

{

txtVerifiedInfo.Text = txtVerifiedInfo.Text +

"\nThe information was successfully saved!";

}

else

{

txtVerifiedInfo.Text = txtVerifiedInfo.Text +

"\nThe information was NOT saved.";

}

Now when I click "continue" my webpage shows this line of code highlighted:

if (clsDataLayer.SavePersonnel(Server.MapPath("PayrollSystem_DB.mdb"),

Any tips? If you need more information I'll give more.