It's always better to uninstall previous beta!
(if You fail to uninstall it erase beta subdirectory inside ARMA 2 directory)
It's recommended to restart You mission instead of using save from older version or previous betas!
Beta installer create shortcut inside ARMA 2 directory to launch beta properly.
The tricky part is that the game is started with commandline:
Drive:Path\ARMA 2\beta\arma2.exe -mod=beta
but in start in path
Installer claims it updating on version 1.04, ignore it updating the \beta\ directory content
Uninstaller claims it removed version 1.03 ignore it as it should remove \beta\ directory content
Uninstalling beta may result into removal of ARMA 2 symlink / junction directory link (hopefully not whole directory)
IF anyone experience whole ARMA 2 directory erase on uninstall please report ASAP thx
FIX / WORKAROUND for the beta failing to install on STEAM build:
use registry editor add registry key into
HKEY_LOCAL_MACHINE\SOFTWARE\Bohemia Interactive Studio\ArmA 2
create new String value
name it "MAIN" (w/o "")
then place into it same content like is already in key "path"
(e.g. "C:\Program Files\Steam\SteamApps\Common\ARMA 2" w/o "" again)
that's all and now the installer sees Your STEAM game ...