If you dowload modules using Safari, it may unzip the file and make it unusable as a .mod.
In General Prefences, make sure 'open "safe" files' is NOT check. Haven't tried other browsers yet, but this had me confused. I am new to the Vassal group; haven't even played a game yet. My best friend just downloaded Vassal also and some mods via safari and we were both confused. Now we can start playing.
