Are not signed by a key accepted by this server problem?

[Are not signed by a key accepted by this server problem?]

Theres a few servers that just kick me with a message saying Are not signed by a key accepted by this server. To play on this server remove listed files or install additional accepted keys. What do can i do to fix this problem?

The screenshot of the error message:

http://puu.sh/bnjuU/076342820a.jpg

[Experienced Aussie looking for a small yet capable squad]

Hey, I'm looking for a serious squad to join.

I'm an experienced player and I know both the chernarus map and lingor map well.

I have skype and also Teamspeak

I live in Australia

Im 16

I'm free to play from 5pm onwards to 11pm on most days of the week

Im quite geared on the public hive with an as50, ghillie and a m249 saw

I've been alive for a good 20 days

At the moment im mostly playing on namalsk servers

[Australian Clan [DT]]

Age:15, quite mature

How often are you on DayZ: 6 days a week

Do you have a mic: Yes,trittion ax720's

Play times:about 4 hours a day

Current Loadout: As50, ghillie, m249saw -all the equipment eg rangefinder gps etc

Ideal loadout: m4a1 cco sd-g17- M24

Last time you died: 2 weeks +

How long have you been playing DayZ: about a month and a half

Do you have much experience with groups in ArmA/DayZ: I usually play with 2 other players, they arn't serious about playing as a team and thats why im trying to join a clan

Skype: Tempest.121

[Serious player looking for a serious Australian clan]

Hey, I'm looking for a Serious clan to join.

I have skype and also Teamspeak

I live in Australia

Im 15 and Yes, I am mature

I don't mind taking any role sniping, scouting or covering, i can handle it

I'm free to play from 5pm onwards to 11pm on most days of the week

I'm quite geared on the public hive with an as50, ghillie and a m249 saw

I prefer playing on large private hives with passwords to avoid hackers and hacked gear

Skype: Tempest.121

[Looking to start a clan!]

Hey, I'm looking for a Serious clan to join.

I have skype and also Teamspeak

I live in Australia

Im 15 and Yes, I am mature

I don't mind taking any role sniping, scouting or covering, i can handle it

I'm free to play from 5pm onwards to 11pm on most days of the week

I've quite geared on the public hive with an as50, ghillie and a m249 saw

I prefer playing on large private hives with passwords to avoid hackers and hacked gear

Skype: Temepst.121

[Looking for a serious Aussie clan]

Hey, I'm looking for a Serious clan to join.

I'm an experienced player and I know both the chernarus map and lingor map well.

I have skype and also Teamspeak

I live in Australia

Im 15 and Yes, I am mature ;)

I don't mind taking any role sniping, scouting or covering, i can handle it

I'm free to play from 5pm onwards to 11pm on most days of the week

I've quite geared on the public hive with an as50, ghillie and a m249 saw

I find all the maps enjoyable

I prefer playing on large private hives with passwords to avoid hackers and hacked gear