I was getting a whole host of errors on even the simplest of web pages or components (aspx or ascx) in Visual Studio 2010 Beta 2.
Validation (): Element 'content' is not supported.
Validation ($SCHEMA$): Element 'div' is not supported.
…and others. Basically, all ASP.NET controls and all HTML tags were not validating. Here’s a shot from a simple page with about 30 controls on it:
The Perils of First Place
It turns out that there was a bug with the user settings from earlier betas of Visual Studio 2010. When you are an early adopter you sometimes have to eat the weird situations of non-workingness. Removing the older IDE would leave behind some zombies that attacked the recognition abilities of Beta 2, thus generating loads of validation warnings.
The webdevtools folks published an article on this which helps. They don’t mention the zombies, but I’m pretty sure they are there.
To get around the problem, simply run Tools –> Import and Export Settings and reset everything. Unless you are particularly attached to something in your user settings don’t bother saving what you currently have. It takes a few moments to reset the IDE…
…and then you’re done.