weird message when joing taviana.eu servers

[SEKROM 2]

I dont know what this is, but when ever I try and join a taviana.eu server it pops up with this big old message saying the i need to delete about 20 files because they're not signed by a key accepted on this server, to play on this server delete the files listed or install addotional keys. But what does that even mean??!? ive never had this problem before. Its only started recently.

So if anyone could help me it would be really helpful because all my mates can play on a taviana.eu server but i cant. And also ive checked the file integrity on steam for arma 2, arma 2 operation arrowhead, plus all the dlc for it as well, and on arma 2, 2 files failed but it said it would re download then or something and the same for arrowhead, and it still says the same thing. So yeah if anyone has had this problem, or knows about this problem and knows how to fix it please post back as its really annoying me!

[BwobBwub 660]

Re-download or re-install taviana

[Nicolaitic 26]

Y U NO TAKE A SCREENSHOT?

[SEKROM 2]

@nicolaitic

i put a photo with it, couldnt get a screenshot

[SEKROM 2]

@bwobbwub

ive uninstalled everything and gonna start afresh