Shopify Facebook App error "another item with the same retailer id was already uploaded...

[donnamac]

We are getting products erring out with this message

   "another item with the same retailer id was already uploaded to this catalog"

We are getting it on products from retailers we have carried for a long time.  
I have tried to report it via the 'report a problem' function with no results.

Can anyone shed any light on what causes this error and how to address it?
The product still gets sent to Facebook, so I am not sure how to 'clear' it in Shopify Facebook app?  The product is not flagged with an error in Facebook.

Thanks