Hi,
there are some problems with C4D shaders that are not supported by Corona. I plan to add a filter for unsupported shaders, but with the current build it's easy to crash Corona with certain shader-setups. This has to be handled by Corona as you are able to crash Corona even if you do it manually.
However, I'm going to add more failure checks to support stability.
Even with 2000 materials, it takes less than a half-second on my machine.
The MaterialConverter is just a script and deprecated, therefore it should not be used anymore. (Use it as long as you want to convert Vray materials though as in the current build of the scene converter, there's no vray support yet - follows with the next update)