Not sure what lemma is doing (never used it ... just played a bit and it seems okay). BTW, my GUI is emacs
The "warning no RC file" is a mma generated warming (nothing to do with lemma). It just informs you that you don't have an rc file. Simple to avoid this is:
cd ~
touch .mmarc
and that should go away (this is an empty file, but mma doesn't care).
the "Failed to generate midi" looks like a lemma error. And is most likely a path problem.
Just a hint on stuff like this ... make sure the underlying progam (mma) is working, then add in the gui.
I just tried lemma on my system and had a bit of a problem. Seems that after changing the settings you need to quit and restart.
To see where/what the "real" error is you should run lemma from a terminal and the error output will display on the screen. This might be helpful?
Please let us know solution, etc.
Best.