输入字符串的格式不正确。 在线等候

public int Insert_WorkPlan()
{
SzrxWeb.classes.Common com=new Common();
SqlConnection con=com.getConn();
con.Open();
SqlCommand cmd=com.getCommand("USP_Inner_Add_WorkPlan",con);


SqlParameter pcreatmanid=cmd.Parameters.Add("@creatermanid",SqlDbType.BigInt);
pcreatmanid.Value=this.Title;

SqlParameter ptitle=cmd.Parameters.Add("@title",SqlDbType.VarChar,100);
ptitle.Value=this.Title;

SqlParameter pdetail=cmd.Parameters.Add("@detail",SqlDbType.VarChar,500);
pdetail.Value=this.Detail;

SqlParameter pstartdate=cmd.Parameters.Add("@stardate",SqlDbType.DateTime);
pstartdate.Value=Convert.ToDateTime(this.StartDate);

SqlParameter penddate=cmd.Parameters.Add("@enddate",SqlDbType.DateTime);
penddate.Value=Convert.ToDateTime(this.EndDate);

int i=cmd.ExecuteNonQuery();
con.Close();
return i;
}