Serious issue.

[Pandora (DayZ) 0]

My ArmA2 version is a steam product and I've got a serious problem. When trying to join a server for the first time, I get in and get "You're running an incorrect version of Day-Z code, the server is running vX.X.X, you're running vX.X.X" (I'm running the latest version, it's the servers that aren't)

Then when I quit the game and reload it, when trying to join it says "You cannot join this mission because it requires game data you have deleted", and I have to recheck the game files in steam.

[Cataclaw 3]

You need to "Right Click" the name in your "Library" in Steam, and choose to run "Combined Arms"

:)

[sherlock (DayZ) 31]

Then when I quit the game and reload it' date=' when trying to join it says "You cannot join this mission because it requires game data you have deleted", and I have to recheck the game files in steam.

[/quote']

There are two possible reasons for this particular error message:

1) as Cataclaw pointed out, make sure that you're running "combined operations"

2) check if all necessary files were downloaded and extracted to your @dayZ/Addons folder within your Arma 2 (opteration arrowhead) folder.

I hope this helps.