Gridless maps should be ok, but you can't use --units|u, because there is no such thing as a unit square for a map with no grid (the page has no conversion factor associated with it). Either use --units|m or leave that line out. Also, you can just use one of the parameters false/no/0 for the --visible command, like --visible|0 or --visible|no. EDIT - Ugh, double checking and it looks like a bug *has* popped up for gridless maps. Apologies, I'll try to get a fix out soon.