Mark,

There was that issue with DPP 4. You had to have a current body. But I thought it was fixed with a recent release. Are you sure you have the latest version of DPP 4?

But, somewhat amazingly, the 1DsIII is not on this list.

I also found this quote: "At launch, DPP 4.0 is compatible with Canon’s current range of full-frame DSLRs, including the EOS-1D X, EOS-1D C, EOS 5D Mark III and EOS 6D. For other models, an update of DPP 3.14 will be released."