I've recently been processng NEFs from a D300 using ACR without any problems. Until...
The following photo has some very wierd red shadows when imported using ACR5.5. But when viewed using the Nikon ViewNX 1.4.0 they look perfectly ok. I've also tried using ACR4.x (the one distributed with PE6) and it's just the same as 5.5. The whole batch of photos taken using this lighting setup show the problem. I was using a Dlte2 on minimum power behind the subject pointing toward the camera and reflectors on the sides. The camera is using the AdobeRGB space.
The problem is most visible under her chin to the right of her hand, and on the hair just up and to the right of there.
I'd really appreciate any insights as to why it appears so "badly" in ACR but looks fine in viewNX and in-camera. And how I might proceed with processing these...
Your shadows are clipping at ACR default of 5. Dragging the black slider to zero should fix the problem.