Comment 4 for bug 1020338

Sorry, I am afraid you are going to have to be more detailed. I am not a Mixxx experienced user, I just bought the Reloop device, installed Mixxx and have not been able to use it yet, to my great frustration:
Do I do this with the Reloop device connected ? if so, do I connect it before or after I launch Mixxx? How exactly should I do the "disable, then reload the Reloop preset" action? I mean, this is what I am doing in an attempt to guess from your brief instructions:
1) With the Reloop device OFF, I launch Mixxx.
2) Then: Options -> Preferences -> MIDI Controllers -> 1. Midi Through Port-0 -> Remove the check mark from the "Enabled" -> click OK. (I am assuming this is what you mean by "Disable the MIDI Through device" part)
3) My interpretation for the "reload the Relooop preset": now I go again: Options -> Preferences -> MIDI Controllers -> 1. Midi Through Port-0 -> put the check mark on the "Enabled" -> click "Load Preset" and select "Reloop Digital Jockey 2 Controller Edition". Then click "Yes" to the "Are you sure?" popup. Then click OK to go back to the main window.
4) Now I switch ON the Reloop device, previously the USB connector is connected.
5) After several seconds, I drag a music to the left side and another music to the right side.
6) If I click on any buttons of the Reloop device, nothing happens.
7) I click any of the play buttons on the GUI and Mixxx crashes and closes.

Next attempt:
1) With the Reloop device still connected and ON, I launch Mixxx (after the crash).
2) Then: Options -> Preferences -> MIDI Controllers -> 1. Midi Through Port-0 -> Remove the check mark from the "Enabled" -> click OK. (I am assuming this is what you mean by "Disable the MIDI Through device" part)
3) My interpretation for the "reload the Relooop preset": now I go again: Options -> Preferences -> MIDI Controllers -> 1. Midi Through Port-0 -> put the check mark on the "Enabled" -> click "Load Preset" and select "Reloop Digital Jockey 2 Controller Edition". Then click "Yes" to the "Are you sure?" popup.
When I do this, I get a series of popup messages like this:
Mixxx - MIDI script function not found
The MIDI script function 'DigitalJockey2Controller.EnableHeadPhone2' was not found in loaded scripts.
The MIDI message 0x90 0x41 will not be bound.
(Click Show Details for hints.) Details:
* Check to see that the function name is spelled correctly in the mapping file (.xml) and script file (.js)
* Check to see that the script file name (.js) is spelled correctly in the mapping file (.xml)

When I click OK, then another popup almost identical, just with different script functions, like 'DigitalJockey2Controller.EnableHeadPhone1', 'DigitalJockey2Controller.LoopIn' and many others that "will not be bound".
4) After clicking OK to all of those, I get to the Midi Through Port-0 page, so I click OK to return to the main window.
5) I drag a music to the left side and another music to the right side.
6) If I click on any buttons of the Reloop device, nothing happens.
7) I click to any of the play buttons (left or right) and to many other buttons on the GUI and Mixxx does NOT crash, it seems to work normally. But no Reloop controller.

Was this what you wanted me to try?
What would you expect to happen by just disabling and then reenabling the Midi port ?

Thank you for your help