ImageMagick API with multi-tasking?

[Hilbert]

I'm trying to invoke two instances of the ImageMagick API, one for foreground and one for background processing. I'm getting errors like:

Assertion failed: (wand != (MagickWand *) NULL), function

...when I try to call the 2nd instance of IM. Has anybody tried to do this, any tricks I should know about to resolve these types of conflicts?
thanks!