I'm working in an ASPX page where intellisense is not functioning. The page compiles and functions correctly - but if I intentionally create a syntax error, instead of placing the message in-line it's being displayed in the top line - the <%@ Page Title="Stuff" Language="C#"...%>
In the same project, but a different page, everything works as expected.
Declaration:
<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Admin.Master" Inherits="System.Web.Mvc.ViewPage<OrderRow>" %>
Curiously have you updated your project from Visual Studio 2005/2008?
Myself and my work colleagues had a similar situation, and I managed to fix it by running devenv.exe /resetuserdata. This completely wiped all my user data (as hinted by the argument!) and so I had re-add my themes, settings and keyboard shortcuts.
It's had varying degrees of success, I'll be honest, but it seems to be quite a serious issue for a lot of developers right now.
Accidentally found the condition that was preventing Intellisense:
The original page had a code block:
<%
=paymentAmt%>
At one point during my editing I collapsed that whitespace for sake of readability to:
<%=paymentAmt%>
Intellisense highlighting reappeared.