Screenshots help a lot as does exact info on your settings, footage origins and types and even what version of AE you are using - all of which you failed to provide thus far, meaning your post is completely devoid of any hard facts.
Sorry about that. The facts are as follows:
I'm using Adobe After Effects CS 5.5 on a Mac. The comp settings are HDTV 1920x1080 25p. The footage used is 'Quicktime' with an 'Animation' codec and a resolution of 1920x1080 25p.
Please find two screenshots below. The first image shows a clip that shows no changes between the preview window and the original footage. The second one has improved skin softness due to noise removal, which gives quite a different appearance when compared to the original footage surrounding the preview.
Have you got any idea why the effect might work on one clip and not on the other?
Is it possible you have temporal filtering enabled in one shjot and not in the other? Also your otehr shot seems to indicate that you are actually sampling the noise distribution from anotehr time, so maybe in your second shot you simply sample beyond the footage duration and naturally it comes up empty?
No, temporal filtering is disabled on both clips. Regarding the sampling, I have tried all versions from source frame 0 to source frame 30 (which is still at the beginning of the footage) and there's no change in there. So I don't think that's what's causing the problem.