Okay. This is a "sig check V2" problem. You are not alone. I also have it, and unfortunately, the options are few. You can try to install and run the Beta patch (found here); I must say, this does not work for me. Perhaps the server would also need to be running Beta patch version? I dunno. You won't have this problem on the Domination server, I can tell you. The work around for this, and this DOES work for me, is to rename your BAF and PMC folders to something like "BAFzzz" and PMCzzz". Now, when you load the game, you will be able to enter the Insurgency server, albeit without the nice textures that the BAF and PMC DLC's add to their items. It sucks, I know, but aparently, those of us with this problem need to use this workaround until the official 1.60 patch is released. Sorry, but we do keep security tight on that server, and a random few do not pass verification checks with their Downloadable Content (BAF/PMC). You will find that the Insurgency server runs the S.O.A.R. map more than the BAF and PMC versions, so you aren't missing much most of the time by loading without your DLC packs. Let me know if any of this works for you.