Since no answer exist for this issue and I have encountered the same error while creating a new "Folder" and "Gallery" in Lightroom Publishing services - only to encounter this error.
I did find a FIX -
* - Edit settings for the Plug In (Assuming this is the item that is having the issue - for me it was)
* - Under the Publishing and Syncing panel make sure "Sync Photos" is check and then click on the "Sync Now" button.
This fixed all for me and all is working as should be now. After doing this, I