I get this error shortly after opening the Reaktor 4 VSTi (carbonized) or placing any audio file on a track. Using Emagic EMI6|2m, Metro 6.06.
This happens sometimes even if I don't have any instrument open in Reaktor yet, so it doesn't need a lot of CPU.
Furthermore, the Stop button in the transport window starts blinking then (like being pressed every second), which doesn't allow to press "play" any more.
Only way to get out of this is do delete the VSTi from the Effects window and selecting one of my external midi-instruments from the popup. Or in case of an audio file, delete that on the respective track.
I had this happen before in 6.0.4 (or maybe 6.0.3, don't remember exactly which version it was).
While I'm at it: Opening the VSTi while a Midi-track with notes is selected, the instrument changes to the name of the VSTi (which is like I expect it), but the VSTi only starts playing when it is selected again in the track popup.
, Achim.