[mkgmap-dev] MapSource cannot transfer

Hi, I have created my latest topo map using Mkgmap r1466. When I install the map in Mapsource everything looks fine. But when I try to transfer a few tiles of the map to my GPS after the "Building map set" stage I get this error: "The map set is approximately 54.6 MB, but only 2048.0 MB is available in the destination. Please choose a smaller map set and try again." I tried a different map (http://wiki.openstreetmap.org/wiki/User:Radfahrer) and it worked fine, so it's not a general problem of my Mapsource installation. Any ideas?