problem rendering in FCP

[arturo]

Hi, I'm trying to cut my RED (shot at 4K) material on FCP, using the small proxies and all. Everything plays fine (the clips show no need to render when played) until I try to render some effect on the footage: it shows the rendering red line, but after I render I get a grey screen when I play, no image at all. It happened in 2 different machines, both Macbook Pros, different effects and footage. Does anyone knows how to solve that?
Any help will be appreciated! Thanks!

[Kaku Ito]

I'm experiencing strangeness when using the small proxies.
M proxies seem to be more reliable. Can you go with that?

[Cüneyt Kaya]

just a wild guess...are your sequence settings redcode?
if yes set them to prores/uncompressed QT nefore rendering