Changing the definition art of a pattern

I'm trying to add a circle to a existing pattern.

Using the following code I get an kBadParamErr.

sAIArt->NewArt( kGroupArt, kPlaceBelowAll, NULL, &patternArt );

sAIPattern->GetPatternArt(patternHandle, &patternArt);

sAIArt->ReorderArt(circleArt, kPlaceInsideOnBottom, patternArt);

sAIPattern->SetPatternArt(patternHandle, patternArt);

What am I doing wrong?
I also tried to reorder the patternArt into another GroupArt. I got an kUntouchableArtObjectErr on the patternArt.

Thanks in advance!