OK, all mysteries are cleared. It turns out that the GRUB-sticks were functional after all, but experienced a conflict with the hardware of the laptop I used to test them on. When I boot another system with a GRUB-stick it works just fine. Strangely enough, that laptop has an antix OS installed on its harddrive which DOES use GRUB as bootloader.

Sorry if I was the cause of some waste of time, and thanks again for your feedback. I'm glad that I did uncover a small problem with the default spacefm mount command. So not all effort was wasted.

Thanks! I am glad you solved it. No need to apologize for posting a strange problem. That's what we are here for! For me at least, strange problems are more welcome than the same questions posted over and over. But we are here for those too.

I'm still curious about the system that won't boot the sticks. Can it boot other ones? Any idea what is going on?

If it wasn't for questions like yours, where would we go to contemplate the meaning of Life? Seriously, it gave some of us a chance to scratch our heads trying to figure out what the problem was. __{{emoticon}}__

@Bitjam: the system is an old (2005) Acer Travelmate 6000 (1Gb Ram, single core Pentium M), retrofitted with a 60 Gb SSD. It won't boot WinXP when I install service pack 2 (conflict with the SSD). WinXP SP1 is OK though but has very limited functionality. The system is slow, but the screen and keyboard are very good. With Antix however it just flies.

I have no problem booting it from USB with the ExtLinux bootloader, but Grub bootloader hangs after displaying two messages on the screen. Not a clue what causes the conflict. Maybe I should try just one more time with another brand of USB sticks, if only out of curiosity. I just got me some new spare ones. It's just that my vacation has ended, and time is precious again...

One more small quirk I noticed in the antix2usb script:

I found that the script (called from the Antix Control Center) fails if the filename of the .iso being used contains a space. Since normally one uses a snapshot for that, and snapshots are automatically given a name without spaces, most users will never notice this. It might be by design for who knows why. But one rarely ever has problems with spaces in filenames, so I came to rely on that. Thought I might as well mention it here.

If it is you that is typing in a name with a space in it, just put a \ before the space, or use a ? instead of the space.

No, I'm not typing the spaces myself. I'm using the gui interface and I select an iso file to use in a filebrowser window. The name of the iso file is written in a text field, but cannot be edited. If that filename contains spaces the script antix2usb stops immediately after being started but without any error message. So it's not clear that the spaces in the filename are the cause of the problem.

Oh, OK. __{{emoticon}}__
It does sound like the script needs to parse the filename and replace the spaces with dashes or underscores.