There is a note regarding the resizing of galleries within Flash container movies in the 'Embedding in Flash' section:
SimpleViewer uses StageScaleMode.NO_SCALE and StageAlign.TOP_LEFT. Check the resize code in the example FLA to see how to handle resizing with these parameters set.
Maybe this will point you in the right direction.
However, if the problem is with the resizing of your background rather than with the resizing of the galleries themselves (which have transparent backgrounds), then this may not help.
As a workaround, perhaps you could use a background image (or color) within the gallery itself and it would then scale with the gallery. This may not be ideal but, unfortunately, I do not have a solution to your problem.
SimpleViewer Support Team