Please accept my sincere apology for the inconvenience. Please get in touch with us at any of the other support channels – https://helpx.adobe.com/support.html . Since this is not a generic issue that we can reproduce at our end, we will need someone to look into your machine to figure out what is going on here.
An error occurred while saving the commentBryony commented
I just had this. If it's because you have a white image on a transparent background - invert it to black and then try. It worked for me.