infopath 2007 submit data via web service to sql 2008

I am trying to submit data from an infopath 2007 form to an sql 2008 database table named "employees".  I have 5 columns in the table which i want populated when the user pushes the submit button on the form.  I made a web service to help with the data transfer which infopath connects to.  the problem i have is that when i push the submit button, i get an error on the form telling me  the following.  After the infopath error message, I have included my web service code. i would appreciate some direction in what i am doing wrong.  thank you.

The query cannot be run for the following DataObject: AddNewEmployee
InfoPath cannot run the specified query.
The SOAP response indicates that an error occurred:

System.Web.Services.Protocols.SoapException: Server was unable to read request. ---> System.InvalidOperationException: There is an error in XML document (1, 424). ---> System.FormatException: Input string was not in a correct format.
   at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
   at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)
   at System.Xml.XmlConvert.ToInt32(String s)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReader1.Read2_Employee(Boolean checkType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReader1.Read3_AddNewEmployee()
   at Microsoft.Xml.Serialization.GeneratedAssembly.ArrayOfObjectSerializer.Deserialize(XmlSerializationReader reader)
   at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
   at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle)
   at System.Web.Services.Protocols.SoapServerProtocol.ReadParameters()
   --- End of inner exception stack trace ---
   at System.Web.Services.Protocols.SoapServerProtocol.ReadParameters()
   at System.Web.Services.Protocols.WebServiceHandler.CoreProcessRequest()

WEBSERVICE CODE (C#)

 using System;
 using System.Web;
 using System.Web.Services;
 using System.Data;
 using System.Data.SqlClient;

public class Service : System.Web.Services.WebService
{
    public struct Employee
    {
        public int EmployeeNumber;
        public String Title;
        public String FirstName;
        public String LastName;
        public Decimal Salary;
    }

    [WebMethod]
    public int AddNewEmployee(Employee employee)
{
  int rowsAffected = 0;
  using (SqlConnection conn = new SqlConnection("Data Source=(local);Initial Catalog=Online_Content;User ID=user;Password=******"))
  {
    SqlCommand cmd = new SqlCommand("INSERT INTO Employees " +
      "(EmployeeNumber, Title, FirstName, LastName, Salary) " +
      "VALUES(@EmployeeNumber, @Title, @FirstName, @LastName, @Salary)", conn);

    cmd.Parameters.AddWithValue("@EmployeeNumber", employee.EmployeeNumber);
    cmd.Parameters.AddWithValue("@Title", employee.Title);
    cmd.Parameters.AddWithValue("@FirstName", employee.FirstName);
    cmd.Parameters.AddWithValue("@LastName", employee.LastName);
    cmd.Parameters.AddWithValue("@Salary", employee.Salary);

    conn.Open();
    rowsAffected = cmd.ExecuteNonQuery();
  }

  return rowsAffected;
  }
}