Falko,
In general this is not reliable. You could get it working but only under very specific circumstances.
My guess is that "OldNP" is *not* an objects-enabled namespace. If that's the case, whenever you try to operate on the returned result set, the operations will fail because they require the class to exist on the target namespace. In the particular case of %ResultSet, it may also be the case that some temporary structures and other constructs are somehow dependent on the namespace where the query ran, hence my comment in the previous paragraph.
HTH,
Ram�n
