Slight intonation issue on 6th string

[MinorKey]

It seems that theres a slight issue with the 6th string on my strat. When I hit the 12th fret it rings high. Ive tried turning the screw anticlockwise until its really loose-surely it should never come loose because of the spring?
So I tried turning it clockwise and retuning the string, still sounds sharp.
http://soundcloud.com/cameraman59/intonation-issue

Could it be a string action issue? The rest of the strings are fine.

[MinorKey]

OK I goofed! Should have turned it the other way...Anyhoo, I think its a string action issue cos I tested each harmonic at the 12th fret with my tuner plugged in and all were showing a little sharp, while still playing ok.