The layer presets you want to load, do they have any parameters connected to macro page?
I haven’t tested this thoroughly so I’m not sure if this is the case but when you load new preset the controls on macro page might still refer to the layer preset that has been removed. This could cause problems. If you look at the Hot Brass instrument all macro page controls are connected to script parameters which in turn handle the parameters of the loaded layer.
Edit
It looks like it’s working if the layer preset doesn’t have its own macro page.
(Which is what you found out already. )
If it does then it crashes. Sometimes I was able to load 2 or 3 presets but then it eventually crashed with “serious error…” message.