I have the following code for my optin form:

<script language="JavaScript">
function checkSub(){
    if (document.signup.email.value.indexOf('@', 0) == -1) {
    alert("Please fill in your valid Email address.\nYour email should be in the following format: [email protected]");
    document.signup.email.focus();
    return false}

    else if (!document.signup.terms.checked) {
    alert("You must read and agree to the terms");
    document.signup.terms.focus();
    return false}

    else { 
    switch(document.signup.extra1.value) {
     case "Platinum":  
             answer = confirm("By clicking OK you confirm that you have\nalready entered  
                 the World Cup Giveaway\nas a Platinum upgrade contributor.\n\nIf you have 
                 not yet entered the giveaway\nclick Cancel.\n\nYou can enter using the 
                 link at the\nbottom of the page.\n\nIf you have already entered the 
                 giveaway\nusing a link other than my invitation link\nyou are not 
                 eligible for this offer.");
          if (!answer) { return false}
          break;
     case "Gold":
          answer = confirm("By clicking OK you confirm that you have\nalready entered  
                the World Cup Giveaway\nas a Gold upgrade contributor.\n\nIf you have not 
                yet entered the giveaway\nclick Cancel.\n\nYou can enter using the link
                at the\nbottom of the page.  \n\nIf you have already entered the
                giveaway\nusing a link other than my invitation link\nyou are not eligible 
                for this offer.");
           if (!answer) { return false}
           break;


     default: 
         alert("You must sign up as a contributor to the \nWorld Cup Giveaway to take 
            advantage of \nthis offer.\n\nPlease click the link at the bottom of this 
            \npage or at the blog post mentioned below \nto sign up.\n\nIf you have 
            already signed up using \nthis link, please select the upgrade level\nyou 
            chose on signup or select \"Free\" if \nyou signed up as a free 
            contributor.\n\nIf you have already entered the giveaway\nusing a link other 
            than my invitation link\nyou are not eligible for this offer.\n\nNote:  This 
            page may not function properly\nif viewed in languages other than English.");
     return false}
    }
    }
</script>

<form action="http://ebizac.com/ar/optin.php" method="post" name="signup" onsubmit="return checkSub()">
    <input type=hidden name="action" value="addlead">
    <input type=hidden name="member" value="2315">
    <input type=hidden name="auto" value="7584">
    <input type=hidden name="thankyou" value="http://plr.forinternetnewbies.com/Offer1">
    <input type=hidden name="resubsetting" value="Y">
    <input type=hidden name="resubredirect" value="">
    <input type=hidden name="invalid_redirect" value="">
    <div style="padding:0 0 0 10px;">
    <table border=0 cellspacing=0 cellpadding=2><tr><td class="label"><font size="2" face="arial, verdana">Name:</font></td><td><input type=text size=20 name="fname"></td></tr>
    <tr><td class="label" width="150"><font size="2" face="arial, verdana">Email address:</font></span></td><td><input type=text size=20 name="email"></td></tr>
    <tr><td class="label"><font size="2" face="arial, verdana">Upgrade Level:</font></td><td><select size=1 name="extra1"><option>Haven't Joined Yet</option><option>Platinum</option><option>Gold</option><option>Silver</option><option>Free</option></td></tr>
    <tr><td></td><td align=center><input type="checkbox" name="terms" value="agree">I agree to the terms as described on the <a href="http://short9.com/blog0522-sp" target="_blank">blog post</a> </td></tr>
    <tr><td></td><td align=center><input type="submit" value="Contribute Now"></td></tr></table></div></form>

Everything does what I expect in Firefox, but in Internet Explorer the switch statement always goes to the default case. I tested with an extra alert(signup.extra1.value) in the default case and it shows an empty string.

What could be the problem here?