What I do:
boinc.exe --dir ..\data\01 --skip_cpu_benchmarks --allow_multiple_clients
C:\data\01>\boinc\boinccmd.exe --project_attach http://setiathome.berkeley.edu my_weak_auth_key_for_SETI

What I get:

Authorization failure: -155

So, what I doing wrong and how to do right?

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boinccmd tries to change current directory to BOINC's data directory and read gui_rpc_auth.cfg from there. In this case the data directory is the one specified in "HKLM\SOFTWARE\Space Sciences Laboratory, U.C. Berkeley\BOINC Setup\DATADIR". If the registry key doesn't exist boinccmd tries "%ALLUSERSPROFILE%\boinc", creating the directory if necessary.

Since you are trying to run multiple client instances probably easiest use password on the command line "boinccmd --passwd password".

I would add "--redirectio" to the client's command line so that log messages are put into a file.

If this is related to your current thread - "BOINC portable" for Windows hosts - at SETI, I presume that you are trying to run on a Windows machine without running the Windows BOINC installer.

If that is the case, none of the registry values normally found in "HKLM\SOFTWARE\Space Sciences Laboratory, U.C. Berkeley\BOINC Setup\" will have been set by the installer. You will be missing INSTALLDIR and DATADIR, among others. Best to use command line parameters for everything you need, as Juha suggests.

So I need to specify password in boinccmd command line and set (or fetch already created one) it into gui_rpc_auth.cfg for boinc to know it. Thanks,I'll try.
And yes, it's part of my experimentations with BOINC's "portability".
Ultimate goal is to create/adapt set of scripts that will allow easely handling number of offline hosts.

Unfortunately, I encountered another issue that looks like bug in boinc client to me (100% CPU usage by boinc.exe). But such issue deserves own thread to be started.

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