There is one error in command line output:
[2014-05-30 11:39:19,564]: WELCOME TO ADDON BUILDER
2014-05-30 11:39:19,564 [INFO] 1: AddonBuilder.Startup.Main - WELCOME TO ADDON BUILDER
[2014-05-30 11:39:19,564]:
==========================================================================
2014-05-30 11:39:19,564 [INFO] 1: AddonBuilder.Startup.Main -
==========================================================================
[2014-05-30 11:39:19,574]: Init Steam failed
System.IO.FileNotFoundException: Could not load file or assembly 'SteamHelper.dll' or one of its dependencies. The specified module could not be found.
File name: 'SteamHelper.dll'
at AddonBuilder.Startup.InitSteam()
at AddonBuilder.Startup.Main(String[] args)
2014-05-30 11:39:19,574 [ERROR] 1: AddonBuilder.Startup.Main - Init Steam failed
System.IO.FileNotFoundException: Could not load file or assembly 'SteamHelper.dll' or one of its dependencies. The specified module could not be found.
File name: 'SteamHelper.dll'
at AddonBuilder.Startup.InitSteam()
at AddonBuilder.Startup.Main(String[] args)
SteamHelper.dll however is there, in the Tools root folder, next to AddonBuilder. Steam integrity check was fine, reinstalled Steam & Tools from scratch, on 2 separate operating systems (both Win7-64). Tried running things as administrator, compatibility modes, nothing worked.