Anyhow, if I had to guess at this point I'd say MLCad is trying to make a temporary copy of your ldr file to pass to lsynth, and it wants to make it somewhere in your home directory structure. But that & is confusing it so maybe it tries to put it in the root directory where it has no permission.
I'd consider changing your username from j&j to something normal like jnj.
I'd consider changing your username from j&j to something normal like jnj.