Today as I was working on a Silverlight application in Visual Studio 2010, XAML Intellisense just stopped working for me.  Quick internet search yielded no useful results, so I was to figure this out on my own.  Just to test I created a brand new application, and Intellisense was fine there.  Logical answer was that there was something wrong with my project.  I re-created the project, and slowly retraced my steps, testing XAML Intellisense  after each step.  The feature broke again as soon as I added a reference to  third party library I downloaded off the internet.  Something wrong with a file, obviously.  What I saw is that the DLL in question was blocked by Windows security.  I unblocked by right-clicking on the file in Windows explorer, going to properties and clicking Unblock button.

The package that I downloaded included many files, and I really hated to go through each one. Next internet search yielded a great solution from SysInternals.  You can download it here.  Once I got streams utility, I ran it on entire folder, and voila – Intellisense was back.  The command line is “streams –s –d ‘Folder with DLLs to Unblock’”, in my case “streams –s –d “c:ThirdParty””

So, my research solved two problems for me – missing XAML Intellisense  and ability to unblock multiple files which is something I wanted to find an answer to a while ago,