If you are running Moles in Visual Studio 2012, you will need to explicitly exclude certain assemblies and types.
Here's what works for me:
<Assembly Name="System.Windows.Forms" ReflectionOnly="true"/>
<StubGeneration>
<Types>
<Clear />
<Add FullName="Your.Type.Full.Name!" />
</Types>
</StubGeneration>
<MoleGeneration>
<Types>
<Clear />
<Add FullName="Your.Type.Full.Name!" />
</Types>
</MoleGeneration>