Shimano 6600 cassette on 7800 freehub

[Jamisrider]

I could swear that everything out there says I should be able to install a 6600 10-speed cassette on a 7800 freehub, but the combined sprocket has a flange that will not fit down over the splines. Am I crazy? Any suggestions?

I could post a picture that would show this condition if it would be helpful.

Thanks,

[cyclerUK]

Are you saying the sprocket won't slide at all onto the freehub - even without the other sprockets in place?
Or the freehub doesn't seem long enough to take the whole cassette.?