When using a Mac, MapInstall will send over ALL maps that you have selected and installed within MapInstall (not just your active map). I also have City Navigator 2010 installed for my Nuvi. Therefore, MapInstall was sending over *all* of the City Navigator map in addition to the Colorado topo maps. The maps it couldn't unlock were the City Navigator ones, not the Colorado ones.
So, if you are using a Mac, make sure that all your other maps are deselected in MapInstall! The software support guy said that he had requested a fix for that problem with later versions, but we'll see.