Good finally it is my couple md1 mcd2 which poses problem !

The only md1 works perfectly, and the error 07 disappears. As soon as my mcd is paired the error comes back and the megadrive reboot...
Another md1 with the same mcd and no problem! I do not understand, probably a concern with the md1.
In any case the x7 is not in question.

I would still like to know what this error 07 corresponds to!

Thank you all