A while ago we posted about a bug that causes players to drop from custom games.
It's probably not the uploading itself which causes errors, but the time players spend in the lobby before they start.
Games which fill up quickly and start usually don't make problems, while games that are slow to fill up drop players more often.
Again, this is only speculation, but several people already pointed this out to me.
NotD: Spec Ops is a hardcore team based survival game. It draws roots from Warcraft III custom games: NotD II and NotD:SO. If you have played them before you should feel very familiar with this one. It is challenging and has a rather steep learning curve, but if you're looking for a nice challenge, a great team game and are not afraid of a few initial setbacks ( = early death ) then you should try it out!
Visit the notdso channel if you want to look for a team to play with.