[mkgmap-dev] "Too many roads"

I am working on a map of France based on Open IGN, OSM and other sources. I have broken it into tiles 0.25 latitude by 0.5 longitude. I built a set of contours using 'marching squares' on the IGN Height data.. But MKGMAP fails on some of the contour tiles saying 'Too many roads' (which I guess is really Too many Polylines). Is this a limit on the number of Polylines (I could join some shorter ones together) or a limit on the number of data points? Thanks, John www.the-thorns.org.uk/46251550.mp