When I run my current 9.3 build in VS2010 using View in Browser, the site works fine.

When I run in debug I get an error in XmlPackage2.cs, line 1110 ...
if (m_DataDocument.SelectSingleNode("/root/Cookies/" + ParamName) == null)

ParamName = .ASPXANONYMOUS

The error heading is XPathException occurred
'/root/Cookies/.ASPXANONYMOUS' has an invalid token.

Any suggestions on what I'm doing wrong?
Thanks