Unresolved references (assemblies)

Using:

Visual Studio 2005 Team Edition for Architects
Extensions for Windows WF
Windows Workflow Foundation Tools for Visual Studio
Orcas Technology Preview - WinFX Development Tools 1.0
Microsoft Visual Studio Code Name Orcas Community Technology Preview -
Development Tools for WinFX
etc.

The beta's are Beta 2 I beleive.

When creating a WinFX windoes application and add a reference to e.g. the
System.dll assembly, it becomes unresolved (warning "The referenced
component 'system' could not be found").

If I create a Forms application instead everything is ok (with the same
references).

Any idea ?