Had this problem ever since using WeBuilder, can't find it using the search, so finally thought I'd post about it.
Basically having an ASP comment and an ASP end tag (%>) on the same line will "break" HTML highlighting & syntax check following it, until the next %> asp end tag.
A couple of images to show better:
This is fine, no problems at all:

Now I've added a comment to line 121, and the %> tag is on the same line. This is valid ASP and doesn't break in other editors:

You'll now see that the ASP tag on line 121 is now grey as part of the comment rather than yellow.
The HTML below is now treated as ASP code and the highlighting changes colours (<html lang="en"> etc)
This happens till the next %> tag on line 124
But now the </title> is red because WeBuilder thinks the <title> tag is ASP code rather than HTML code.
This can be rather annoying if there is a large block of HTML till the next found %> tag as all the HTML will be coloured wrong and the highlighting of matching & missing HTML tags no longer works.
Cheers,
Mike