My chain rubs on the front mech when its in the middle ring and the highest gear at the back. I've tried fiddling with the adjuster screws but its not made any difference.
Any suggestions on how to fix it other than avoid that gear? (its starting to drive me up the wall!)

Simplest answer is to avoid that gear.

Unless you want to faff around for ages tuning your chainline, stick to the rule of thumb of there being 2 gears you can't use on the block for any particular front cog:
granny ring – don't use 2 smallest.
middle ring – don't use the extreme cog at either end.
big ring – don't use the 2 largest.

Dave

That's what happens.
Don't run that gear if it annoys you (plus, it's not very good for your chain anyway, due to the large deviation. You better off dropping to the small chainring + 3rd on the back).

The H/L adjuster screws is for setting the min and max setting on the small and large chainrings, to stop the chain over shifitng on those two gears.

The Parks website is good to show you how to set things up:

http://www.parktool.com/repair/readhowto.asp?id=75

Avoiding that gear it is, I did think it might be slightly pushing it but was worth a shot!

And yeah – the parktool site is great for stuff like that!

get a gripshifter for the front and enjoy more mech positions ?