I had the same (or very similar) issue.
I also deleted some (but not all) files in the folder
C:\Documents and Settings[username]\Application Data\Microsoft\VisualStudio\9.0\ReflectedSchemas
The reason I did this is because I'm subject to a frankly daft limit on the size of my (Windows XP) roaming profile :-(
After I did this VS intellisense and document auto-formatting started behaving as if it didn't know what the <asp: tags were and treated all the html as plain html (formatted tag names and attributes in lowercase).
I found this blog post by Tim Vasil which pointed me to the solution.
Here's what I did to fix this:
Deleted all files in C:\Documents
and Settings[username]\Application
Data\Microsoft\VisualStudio\9.0\ReflectedSchemas
Deleted all files in
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary
ASP.NET Files
- Deleted the .suo User Option file (the file has the same name as the solution file with .suo in place of .sln)
(Note: VS eventually regenerates the various files in it's own time...)