Product Variations Add-On Error

This Add-On allows to create products with different feature variants (for example, a different color or size), and let customers select the desired variant.
When I am using this add-on and saving the pictures as URL, saving gives me this: Error File could not be uploaded
I can’t upload a picture using the URL option and I have to select a file from a Local folder.
If I do so, it will load correctly, but it is not very convenient.
Does anyone know how to fix this problem?

Are you able to import other image url’s (like product images) from the same domain? If not, you may have the same issue as described in this post.