Document location href problem

[admin]

Here's a js function:
function somefunction( MembershipLevel ) {

if (MembershipLevel == 1) {
var wc=window.confirm("Messages can only be read by Gold members. Click OK to upgrade to Gold status");
if (wc == true) {
document.location.href='MembersArea.jsp';
}
}

When Ok is clicked on the confirm window, the page doesn't proceed to MembersArea.jsp. I've tested the condition which is passing MembershipLevel okay, wc returns true and if(wc==true) is entered but document.location.href... does not perform the command.
I've run this elsewhere slightly differently which works okay.

Why doesn't document.location.href="MembersArea.jsp" work ???

Any help appreciated.

Thanks