A style may consist of up to 8 parts, such as Rhy1, Rhy2, Bass etc.
But every part can internally consist of more than one midi track. Of coarse the number of midi channels is limited to 16. So it may happen, when parts from different styles are copied into one style, that all 16 midi channels are already occupied. In that case the "out of memory" message occurs. The message is misleading, it should read: out of midi channels, because there are not more than 16 midi channels on one cable or within one style or one midi file.