By deleting the lastexit files, you are telling the program that you are a new user, that DB has never been run on that computer. I'm not sure why you are doing this (you can always load a sim after startup) but I made the recent change (by request) to have internet mode be the default mode for new users. If there is no lastext.sim, I automatically enter internet mode at startup. If there is, I don't.
What you are seeing via your firewall w.r.t. DB trying to communicate on the network when disabling IM is expected. When you hit the IM button to leave IM, I attempt to delete the population file on the server for your sim as you are disconnecting from the megasim and I need to tell all the other sims your are leaving, so yes, communication on the network is attempted when you leave IM (or quit the program while in IM). If you leave IM immediatly after entering IM, before 100 cycles typically, this attempt may be the first network communication attempted by DB.
The crashes are still very valid bugs, probably have to do with trying to close the Internet graphs when they arn't open. In the new user start up path, I don't automatically open the internet mode log or populations graph so as to make the first time expereince as clean as possible. I am probably trying to close them when they arn't open or somethign similar and this is the crash you are seeing. I'll take a look, but if you figure out a deterministic way to cause the crashes, that would be useful.