Hi Laurent,
Work on linux sysex transfers is being done in the beta version (New ElectraOne console / Testing needed - #17 by RobinC).
The problem is that the ALSA driver does not handle sysex messsages larger than 4kb. I am not saying that it is a general problem of the ALSA driver. It can be something specific to Electra USB interface. If you attempt to transfer such a preset (I mean larger one) it will produce the inconsistent data in the controller and will result in an unexpected behaviour.
To get your Electra working again, please do following: disconnect Electra from the USB. Press and hold the left-middle button. While holding the button pressed, connect Electra to the USB. Keep the button pressed till the start up progress bar is on 100%. This procedure will remove the broken preset file.
When you restart Electra now it should boot up. Of course there will be no preset as it was removed.
At this moment you will be able to load the presets on MacOS X or Windows. On Linux, you should be able to load a preset that is under 4kb. That equals to, say, a preset with one or two controls.
For using Linux, definitely upgrade to the beta release of the firmware. I and @thetechnobear are trying to get sysex working on Linux. And this work is being is being done in beta. There are a few things we achived so far:
Increasing the output_buffer_size parameter of snd_seq_midi kernel module, you will be able to upload larger presets.
I do believe that @thetechnobear found that this problem can be worked around when communicating with raw midi instead of the ALSA driver.
We are also discussing an option to break large preset trasfer sysexes to number of smaller messages.
I am using Ubuntu. When I adjust the output_buffer_size Electra works perfectly. I do not consider this solution as optimal, so more work needs to be done. If you have deeper experience with MIDI on Linux I am happy to share details of my findings.
If you had troubles with removing the preset or if you wanted to discuss it, please reach me on the website chat.