As per the above link, there's supposedly 3 DLLs that come with the download that need to be referenced.
The AntiXSS Sanitizer Provider is included in the SanitizerProviders folder with the CodePlex release of the Ajax Control Toolkit. You need to add a reference to all three assemblies contained in the folder: SanitizerProviders.dll, AntiXSSLibrary.dll, and HtmlSanitizationLibrary.dll.
However, after downloading the library from http://ajaxcontroltoolkit.codeplex.com/, I only see 2 DLLs in the SanitizerProviders folder:
- HtmlAgilityPack.dll
- SanitizerProviders.dll
Where is that AntiXSS DLL located?