Try to add this statement on the first line in your view:
@using Webdiyer.WebControls.Mvc
Do you use the MvcPager code files in your project? Or do you have them as a separate project that you compile into a dll? If you have them in your own project you have to put them in the right folder. You can create a folder named MvcPager and put all of them there. If you put the files in the wrong folder they might not compile and then you can't use them.