PMDG 747-400X incompatible with Horizon's UK VFR scener...

I've been having problems with the autoland on the PMDG 747-400X. Although the ILS localiser and glideslope were being picked up by the PFD correctly, the autoland tracked the localiser about a half-dot to the left, with the result that the 747 landed on the grass between the runway and the taxiway. It's a weird problem because the ILS is being correctly received and displayed; if you centre the bars and manually fly down the beams, you achieve a perfect touchdown; it's the autoland that misinterprets the signals.What's even weirder is that it appears that the problem is linked to an incompatibility between the 747 and Horizon's UK VFR scenery.I've tried all the usual processes of elimination, going back to a clean install and then reinstalling bit by bit. It's only when I add the Horizon scenery that the problem occurs. And once it's occurred, the only way of restoring autoland is to completely uninstall FSX and start again. By 'completely' I mean just that - I have to clear my temp directories for it to work, and manually delete folders left by the uninstaller.It's not enough to disable or delete the Horizon scenery - it seems to corrupt some nav file somewhere. And the corruption isn't restricted to areas covered by the Horizon scenery - it happens in Scotland and North America.I have another problem that I think is caused by a conflict with Acceleration. With Acceleration installed, the spoilers and thrust reversers on the 747-400X don't show properly on replay. With Acceleration uninstalled, even with SP2 installed, the replay works fine.Does anyone have any idea what on earth might be causing these problems, and how I fix them?Thanks!Stu