I'm having the same problem in several laptops with ACR telling me there's insuffient memory while it's saving changes in ACR. This happens when I open, change, save, and close NEF or jpg images then open another set of about 25 and do the same process. After about the third time, I get the insuffient memory message and I have to close down Photoshop and reopen. This clears it until I do another 3-4 sets of photos then I have to close it down again. Is there a cache somewhere that isn't emptying? It happens whether I save one image at a time or the whole set at once. The problem occurs in different brands of laptops, all with XP Pro, from 2 months to 2 years old, even with a 500gb drive attached for more scratch space, memory is allocated at 70% for Photoshop, and happens with CS3, CS3 ext, and CS4, all w/updated ACR. Memory and RAM isn't an issue on any of the computers. No other programs open. I'm out of ideas. Anyone??
ACR and PS compete for the same memory, try turning down the allocation from 70 to 60 or maybe 50% and see if the issue goes away. Also, do you have any other plug-ins loaded that may be hogging memory?
Hope that helps-