Function To Save Selected Background In Cookie?

I've been researching cookies a bit, and I attempted to create a function that if you select a background name from a drop down list or anything for that matter, it will save the background in the cookie, and display it in a div background for later use. Now I can't quite figure out why there is a problem with this script, but the error checker tells me there is.

Heres the code:
<script type="text/javascript">
//Get Cookie
function get_cookie(Name) {
var search = Name + "="
var returnvalue = "";
if (document.cookie.length > 0) {
offset = document.cookie.indexOf(search)
// if cookie exists
if (offset != -1) {
offset += search.length
// set index of beginning of value
end = document.cookie.indexOf(";", offset); .....