Dat zijn rare foutmeldingen. Probeer inderdaad eerst de andere packages opnieuw te installeren.
Als dat niet helpt kan ik je mijn kopie van RF sturen, die werkt prima onder FontLab 5.1.4 (4868) en Yosemite.
Ikarus is great when you already have perfect technical drawings in a large size (~20 cm tall). Then you can digitise these drawings very quickly, and very accurately.
But to make these kinds of technical drawings is costly – it requires a lot of time and precision from the human hand. Also, in the case of a text typeface it is hard to judge what your shapes are actually going to look like in 8 pt. when you need to draw them first in a big size (in pencil contours!).
For me, the process of designing type is much more dynamic. I usually sketch my first ideas on paper, and may draw some particular shapes in a bigger size (~8 cm tall) in black ink. Then using a scanner, or sometimes just by looking at the drawings by eye, I digitise these shapes in beziers in a font editor and start building the basic character set step by step. A lot of printing in various sizes is part of the process as well to judge the shapes and the spacing.
I still don’t see a difference between libre and non-libre fonts in relationship to web assets. The biggest difference is just the fee that needs to be paid in order to use, or modify the font in question. If libre fonts are used in a commercial environment, they do compete directly with non-libre fonts.