In the past I successfully designed user interfaces and exported .png assets directly from InDesign via the option Export > HTML (InDesign would create an HTML file and an images folder with all assets saved as .png).
I'm trying this now for the first time with InDesign CC 2015 and I'm getting the following message "The file was exported but one or more problems were detected: Non rectangular objects will not appear correctly when exported using CSS." Then InDesign exports the HTML file but none of the images.
In this case most images were icons designed on illustrator and copied into InDesign. This is exactly the same workflow I've used in the past, so I'm not sure if this feature is no longer available. Does anyone has an advice?