I downloaded NW topos as well and it seemed to run fine on my PC with an older mapsource version (5.4 or something like that). Now I upgraded to version 6.x and it always locks up on me. Either way, I couldn't figure out how to install the NW topos on my Garmin 60 CSx. Only Ibycus is on there presently.
So your Mapsource does not run at all now? Or does it intermittently hang? I'm using Mapsource 6.16.3 and Northwest Topos without problems. To send the maps to the GPS, use the Map Tool, click on the maps you want to send to the GPS, then go Transfer, Send to device.
now I am using MotionX app with pre-loaded gpx file and pre-loaded the related topo map (great and free! )and put my Garmin GPS into my backpack as a safety backup. very good!
I usually put my iphone into a ziploc bag in a wet day and bring extra battery with me
here is what I put on CROSSNA, Although it's in Chinese but you can still watch the informative youtubes video that I found online