Javascript error

When clicking on a star, Opera gives the following error:

JavaScript - http://www.fmbv.nu/
Unknown thread
Error:
name: TypeError
message: Statement on line 1: Type mismatch (usually a non-object value used where an object is required)
Backtrace:
Line 1 of eval script
if (context && context.nodeType == undefined)
context = context || document;
if (t.constructor != String)
if (! t.indexOf("//"))
else
var ret = [context];
var done = [];
var last = null;
while (t.length > 0 && last != t)
if (ret && ret[0] == context)
done = jQuery.merge(done, ret);
return done;
Line 1 of eval script
return jQuery.find(t, a);
Line 1 of eval script
if (typeof fn == "string")
var result = [];
for (var i = 0;i < elems.length;i++)
return result;
Line 1 of eval script
return this.pushStack(jQuery.map(this, (function (a)
{
return jQuery.find(t, a);
}
)), arguments);
Line 1 of eval script
if (a && typeof a == "function" && jQuery.fn.ready && ! a.nodeType && a[0] == undefined)
a = a || document;
if (a.jquery)
if (c && c.jquery)
if (window == this)
if (typeof a == "string")
this.set(a.constructor == Array || a.length && a != window && ! a.nodeType && a[0] != undefined && a[0].nodeType ? jQuery.merge(a, []) : jQuery.find(a, c));
var fn = arguments[(arguments.length - 1)];
if (fn && typeof fn == "function")
return this;
Line 161 of linked script http://www.fmbv.nu/modules/fivestar/jquery.rating.js
returnObj.result.count = $("count", $(data)).text();
Line 1 of eval script
if (xml && (xml.readyState == 4 || isTimeout == "timeout"))
At unknown location
[statement source code not available]

IE7 gives "Error on line 162, char 8, Object doesn't support this property or method."
Submitting in Firefox 2.0.0.3 works fine, the votes register etc...