The problem you're having is that your replacement is insufficiently precise. You're replacing ALL instances of </body>
on ALL pages with a string containing quotation marks. However, in some of the instances, the string you're replacing is appearing within JavaScript strings in the Google application, and as a consequence you're mangling the JavaScript string and causing a script error.
Use the following script sample to get a better understanding of all of the places you're replacing, then update your script to more specifically replace the expected string on only the expected page.
oSession.utilDecodeResponse();
if (oSession.utilReplaceInResponse("</body>", '<!-- INJECTED --></body>'))
{
oSession["ui-backcolor"] = "lime";
}