VS2010, solution pointing at ASPNet4.0 website, odd seemingly inaccurate compile error

Hi...

I've got a VS2010 solution point at a website running under ASPNet 4.0.  The code and the website run fine, but when I'm in VS and click Rebuild Solution, I get a spurious error message that flashes by "The type or namespace var could not be found."

Now, I do have a statement

var x = webService.GetData();

in my C# code, but that's legal with any framework > 2...

Aspnet_compiler builds the code without any complaints.  I'm just wondering why VS is throwing this spurious exception...  Any ideas?

Thanks

Mark