Hi Jens,
Max size is 256 MB.
The 256 MB is because the util-files constitute one large virtual file of 4 GB which is divided into 16 parts.
The 12 of them will be used for each of the util-layers.
In principle there are 4 util-layers to spare.
You may move parts of the USR layer over in USP layer, and run in USP layer (-$USP) so that the USR layer do not grow further when the size is reduced.
You probably have to rebuild the USR layer, in order to reduce the size.
/Henrik Hansen