removing project dependencies

I have some Dll's in my web project which is within a Solution. I want to get
rid off one DLL that was added by mistake but it keeps coming back. When I right
click on the solution I can click on the Configuration Manager, Project
Dependencies or Properties. Click Project Dependencies I can pick from the drop
down my web project and see all the dependencies. When I try to uncheck the box
to the DLL I don't want anymore I get the following message:

This dependency was added by the project system and can not be removed. I just
want to delete/remove the DAL.dll from the web project and add it to the BLL
class library but it keep coming back in the bin folder of the web project. I
delete all the dll's for all the class libraries and projects in the solution.
Still it is coming back. I am running Visual Studio 2008 and Vista Ultimate for
the last 10 days and I can't find the Temporary ASP.Net folder. So I don't know
where else it might be cached or hanging on to some references.