Check the path to buldozer in object builder options.
Also check if P: drive is set up properly in case you use it.

helped fully reinstall

Is your issue solved?

Also, I invite you to consult the manual of Buldozer, it should provide you more information about its installation and update process: https://community.bistudio.com/wiki/Buldozer_Manual

I get this message, too, but after it begins to load, but I am using Windows 7.

The ArmaIII logo shows up, then it crashes, THEN I get this attach failed message.

• The steam_appid.txt is in place with 107410.
• My buldozer.exe is located in P:\ (which is E:\Program Files (x86)\Steam\SteamApps\common\Arma 3 Tools\buldozer.exe).
• In Object builder options, the path is set to P:\buldozer.exe, and the cfg is given the same path.

Could you, please, update your buldozer installation?

dev.bat -update

I am getting a similar situation. I start Buldozer, it pops up the viewer window but the "Searching External Viewer" window stays. If I don't do anything, it will eventually fail.

However, when I press Alt-Tab once then press LWin-Tab to bring up the list of windows, I see a "Viewer Search" window pop up from time to time in the list. When I click that while it is visible, the viewer connects and shows the correct model.

This is under Windows 10.

Edit: Per request, moved this to a separate ticket http://feedback.arma3.com/view.php?id=27026