I had someone suggest that your leksah needs to be compiled with the same version of GHC as the one you have on your system. I haven't tried it, but even if it's true, I think that is really silly and shows that leksah may not be mature enough yet, at least not for my comfort. Not to mention that this could easily be detected and the user notified.
So, I ended up using Eclipse FP, which works great.