I had the same problem, which I realised was only happening with products that were also on Google Base. You can get rid of the error by going into System -> Configuration -> Google API -> Google Base and set “Update Google Base item when product is updated” to “No”
Thanks for suggestion… doesn’t make any difference for me :-(
I do not think this is an actual error. I think it means that the items are not found in your g/Merchant account so you cannot edit them via the Magento back-end. Try loogging into your g/Merchant account and see if that is the case.