Question : ASP app reference problem

Hi,
I have a c# asp.net 2010 app, I have defined a basepage class defined like this:

namespace LSFramework
{
    public partial class BasePage : System.Web.UI.Page

and my other pages inherit from that one like this

namespace LSFramework
{
    public partial class _Default : LSFramework.BasePage
    {

Everything works fine but I regularly get the error below after I have been coding and then try to run, the only solution is to "Rebuild Website" then it works again.

"The type or namespace name 'BasePage' does not exist in the namespace 'LSFramework' (are you missing an assembly reference?)"

Answer : ASP app reference problem

I get the same thing on occassion, I believe it is a bug in VS 2010.