Comment 8 for bug 545033

I found the cause! I always install the latest ntfs-3g driver. Colin, you mentioned those files should be available. It seems, that ntfs-3g 2010.3.6AR2 (thus the advanced release) triggers a fail in os-prober: it does not find my W7 partition correctly.
However, downgrading to 2010.3.6 (from source) or 2009.4.4 (package in Lucid) solves my problem!
I will report this problem to the developers of ntfs-3g.