Web Matrix insert command "System.FormatException: 0 : - Input string was not in a correct format"

I am having a problem inserting to DB when I use more than 2 variables.

var answer1 = Request["result1"];
var answer2 = Request["result2"];
var answer3 = Request["result3"];
var answer4 = Request["result4"];
var answer5 = Request["result5"];
var answer6 = Request["result6"];
var answer7 = Request["result7"];
var answer8 = Request["result8"];
var answer9 = Request["result9"];
var answer10 = Request["result10"];
var answer11 = Request["result11"];
var answer12 = Request["result12"];
var answer13 = Request["result13"];
var answer14 = Request["result14"];
var answer15 = Request["result15"];
var answer16 = Request["result16"];

string disabled = "";

if(IsPost && Validation.IsValid()){
   if( Request.Form["submitbutton1"] != null) {
            var insertCommand = "INSERT INTO Answers(Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, Q11, Q12, Q13, Q14, Q15, Q16) VALUES (@0, @1, @2, @3, @4, @5, @6, @7, @8, @9, @10, @11, @12, @13, @14, @15)";
            db.Execute(insertCommand, answer1, answer2, answer3, answer4, answer5, answer6, answer7, answer8, answer9, answer10, answer11, answer12, answer13, answer14, answer15, answer16); 

Any reason I cannot add all these variables? All datatypes are correct, i.e. int or nvarchar for each variable. Please help! I can provide more info if needed.