i have one more relevant info regarding this issue which may help you to solve this problem...
... this error is raised only when using cuteeditor with firefox
Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.9.0.5) Gecko/2008120122 Firefox/3.0.5
Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; de; rv:1.9.0.5) Gecko/2008120121 Firefox/3.0.5
hope it helps