I'm sorry if i'm bumping this, but we are having the same issue. We just upgraded to Acrobat XI, and after saving a spearated PS file, and trying to process it with Distiller, it fails, and gives this error message:
%%[ Error: undefined; OffendingCommand: Adobe_AGM_OnHost_Seps ]%%
%%[ Flushing: rest of job (to end-of-file) will be ignored ]%%
%%[ Warning: PostScript error. No PDF file produced. ] %%