The problem is you are using an outdated version of Camera Raw...as of ACR 7, they added a fully functional defringing control vastly better than the manual sliders in ACR 6.6.
ACR 6.7 was a crossover bridging release to give compatibility to LR 4. So, you are rather behind...and truth be told, this is way, way old news...each version of ACR/LR keeps getting more and more functionality. If you care about image quality, I suggest you look into upgrading.
Thank you for providing the info.
As it happens I do care about image quality, but unfortunately I care also about whether I have any money or not...
jeeez, amateurs eh!?
To be fair, on the basis of conversions so far, "auto" CA correction does seem to work very well.
On the other hand, it would have been nice to have been warned that functionality was going to be potentially
lost by upgrading.
Clearer, better 'customer service' always tends to make the customer less irritated and more inclined to spend
yet more money, and thus be ever more 'rewarded'.