Thanks for figuring this out Michael! And again I learned something new.
Instead of

Draw circle on xz (Front) plane

script:
var frame = moi.vectorMath.createFrame(
		moi.vectorMath.createPoint( 0, 0, 0 ),
		moi.vectorMath.createPoint( 1, 0, 0 ),
		moi.vectorMath.createPoint( 0, 0, 1 ) );
var factory = moi.command.createFactory( 'circle' );
factory.setInput( 1, frame );
factory.setInput( 3, 10 );
factory.commit();

I'll now use the much simpler

script:
var factory = moi.command.createFactory( 'circle' );
factory.setInput( 1, moi.vectorMath.createFrontFrame() );
factory.setInput( 3, 10 );
factory.commit();

Edit: The former script is still required if the center of the circle has to be elsewhere.
The line moi.vectorMath.createPoint( 0, 0, 0 ) determines the center.