Strange bugg with asp.net in Visual Studio

Hi,
I would appreciates some hints or help regarding a strange behaviour in visual studio dotnet when using asp.net. I'm working with authentication and somewhere in the process the framework goes nuts. Let me explain the behaviour for you.
First you have a register page in the root of your project. Next you have a folder named MemberPages and in this folder a login.aspx page. And then you have welcome.aspx page.
You have a web.config and set restricion for anonymous users that redirect to the login page.
If you compile and run the project you get the following error:
Could not load type 'GrundSys01.MemberPages.login'.
Ok and then you remove the login.aspx and rename the folder to MyPages and then add a new login.aspx page and set it to start page.
Compile and run the project. Page displays fine.

Now why is that and what do I need to do?
I have tried to remove temporary files in framwork folder without success.

I would appreciate if you could spend a little time to help me on this.

Regards
Andla