Encounter No Parameterless Constructor Defined ... During The OnObjectCreated Of An ObjectDataSource

I got the following error when trying to pass a parameter from an ObjectDataSource to a BLL during the OnObjectCreated event:No parameterless constructor defined for this object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.MissingMethodException: No parameterless constructor defined for this object.The ObjectDataSource in the aspx is as follows:
<asp:ObjectDataSource ID="LoadData" runat="server" SelectMethod="GetData" TypeName="Export00.Export" OnObjectCreated="SrcObjectCreating">            </asp:ObjectDataSource>
 The code behind in aspx.cs is as follows: 
protected void SrcObjectCreating(object sender, ObjectDataSourceEventArgs e)       
{            Export sqlcommand = new Export("SELECT [DocTitle], [DocID] FROM [Document]");            e.ObjectInstance = sqlcommand;
}  
 The BLL is as follows: Export.cs   (this is the BLL)
namespace Export00{    public class Export    {        private readonly string connString;        private readonly string sqlCommand;public Export(string command)        {    sqlCommand = command;            connString = WebConfigurationManager.ConnectionStrings["MyConnString"].ConnectionString;        }     } 
}Can someone tell me why am I getting this constructor error and how to resolve it? Thanks in advance.sg2000