Steam

You do not have to be always online. You can launch the game with Steam in offline mode.

If you want to switch to the offline mode please click on Steam (top right corner in your Steam window).

Select "Go Offline..."

And restart your Steam client.

Please note that you will not be able to play multiplayer while in offline mode.

You can also switch auto-updating feature of the Steam off:

Right click the game in your Steam library.

Select "Properties"

Under the "UPDATES" you can change settings for automatic updates

Please note that most of the servers will run on the latest version of the game.

Before you start, make sure you have done the following:

Have Steam running as an Administrator

Have the Arma 2 and Arma 2 Operation Arrowhead installed.

If you did all of the above you should now download the DLC files from as you would with any other Steam game (go to your library, select the desired product and click "install"). After the download finishes, click "play" and the DLc should automatically install the remaining files necessary for you to play it. Alternatively, you can just start your Arma 2 Operation Arrowhead. It should detect the DLC files automaticaaly and install them by itself before launching.

Please note that the Arma 2: Army of the Czech Republic DLC will not appear in your steam library as the other two DLCs do. Instead, it will be included in your Arma 2 Operation Arrowhead directly (you should still see the install window during your first time launch though).

There are several possible fixes for this issue.

First, run Arma 2 once. Then try to run Arma ACR (without beta or DayZ).  If that won't help you can try to verify game cache of the Arma 2 and Arma OA.

1.) If that will not help, follow this guide:

1. RUN STEAM AS ADMINISTRATOR
2. Exit Steam.
3. Right-click on Steam icon.
4. Left-click on "Run As Administrator".
5. If the problem persists, reboot your computer and try the procedure again.

2.) DELETE ARMA 2 ACR REGISTRY ENTRIES

1. Exit Steam, open Start menu and type this directly into the menu (in Windows XP, you will have to click on "Run" first) regedit
2. Press Enter.
3. In regedit window, click on HKEY_LOCAL_MACHINE.
4. Press CTRL+F to bring up search.
5. Look for "ArmA" (without the quotes).
6. Delete all the "ArmA" entries you find from the registry.
7. Run Steam as Administrator.
8. Right-click on the game in Steam Library.
9. Click on "Properties".
10. Select "Local files" tab and click on "Verify integrity of game cache files" button.
11. Please wait, the process can take several minutes.

3) REINSTALL STEAM

1. Go to Steam's installation folder.
2. Delete everything there except "steam.exe" and "steamapps" folder.
3. Run "steam.exe" - Steam will reinstall itself automatically.

We contacted Steam regarding this problem and Steam recommended this steps:

1] Exit Steam.

2] Open Internet Explorer, Safari or Firefox and type steam://flushconfig then press Enter. (If asked to allow this website to open a program, please click 'Allow' or 'OK')

3] When prompted by Steam to reset your configuration, click 'OK' to confirm.

4] Once done, you need to login to Steam.

5] Now please completely uninstall and reinstall the game and retest the issue.

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Side note: in case of multiple installation folders for games doing this process will remove them and you will need to add the folders again in Steam so that your games will appear as installed.

In order to add these extra installation folders please do this:

1] Open Steam
2] Click Steam > Settings (Preferences on Mac)
3] Navigate to the 'Downloads' tab
4] Click the 'Steam Library Folders' button
5] Click on 'Add Library Folder' and add the directory that contains your games
6] Click 'OK'
7] Restart Steam

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It is also a good idea to make sure your network is properly optimized for Steam:

Title: Troubleshooting Network Connectivity
Link: http://support.steampowered.com/kb_article.php?ref=1456-EUDN-2493

Additionally, disabling any programs from this guide may also help with the issue:

Title: Programs Which May Interfere with Steam
Link: http://support.steampowered.com/kb_article.php?ref=9828-SFLZ-9289