There are many posts on various forums that state that you need to add a couple lines to your web config to avoid this error. MOst refer to the
<sanitizer defaultProvider="AntiXssSanitizerProvider"
Yet that appears to have been replaced by another sanitizer called - HTMLAgilityPack. I have that and a sanitizers dll in my bin but nno mater how I have tried adding the suggested references to the config file I get this error, or the sanitizer reference in the config file is underlined as an error. Does any one know how to configure this to work?