Hi emgi,
I broke my login system too. Difference is that I have no RPi — instead I use regular SliTaz Rolling installed on my netbook. One beautiful day after updating something brokes and I get the same message "Failed to execute..." and I can't fix it for months :) I plan to re-install my SliTaz from scratch some day, and now I get my desktop this way:
I switched off SLiM start at boot using tazx.
But now you want to stop SLiM. Switch to free console using Ctrl+Alt+F1 or Ctrl+Alt+F2. Log in as root and execute command: killall slim
Next I log in to Linux console as user.
Enter "startx" command and get desktop with completely black screen and lonely mouse pointer on it.
Right click — Openbox menu — Favorite applications — Terminal. Here I start what I need to complete my desktop. Seems like SliTaz @ RPi have no Openbox, yeah? You can type several commands using "&" as separator. So, my complete one-liner to get my SliTaz desktop is:
startx & dbus-launch pcmanfm --desktop & lxpanel -p slitaz &
SliTaz @ RPi possible have different desktop applications. But you can use this technique (with corresponding applications) to log into your desktop.
And... No one works on Spk debugging these days...