Javascript href error

I have a form which needs to go to two different pages depending on the input from the user. My code seems to be working, in that the browser is being directed to the correct pages. The problem is that when the action is completed, the brower gives a HTTP 500 error indicating that the html doc was not found. The address to the file is correct and I double checked to make sure the pages were on the server. If I hit the refresh button, the correct page appears.

Is there something in my code that could be causing this?

function checkform(){

if ((document.form1.category[0].checked == true) && (document.form1.subcategory[0].checked == true))
{
form1.setAttribute("action","correct.htm");
}
else {
form1.setAttribute("action","incorrect.htm");
}
}
</script>