Don't uninstall, Jude, just reinstall right over the existing installation.

When you say the foliage shot back up into the air on the seventh rendering (or so), did you change anything?  I know you're putting in the little house so are you putting that in first and then adding the trees?  The only thing I can think of is that the trees are becoming ungrouped for some reason.

Can you send me a screenshot of your render options?  This will give me a better idea of what you're rendering at.

Hugz from Phoenix, USA

Victoria

Remember, sometimes the dragon wins. Correction: MOST times.