Only had this issue with version 1.2.4 - model uploads, then goes onto processing, then at end of processing normally PS displays the url of the model on sketchfab but instead there is the following error message:
Can't upload model: Unknown error (200)
{"result": true, "sucess":true}
Photoscan Standard 1.2.4 , winX64
But model has successfully uploaded to sketchfab - so there doesn't appear to be a real problem.