The Asset Stack is listed on the Upload Files page displayed below. The first image becomes the thumbnail and a small Asset Stack icon appears on its lower right corner to indicate that it is an Asset Stack, rather than a standard Asset. Balance your mouse over the preview icon and you can scroll through the assets listed in the asset stack using the Next and Previous buttons.
All the Asset upload errors mentioned on the Upload Assets page also apply to Asset Stacks.
When uploading an asset stack, all the files selected in the stack must be valid file types. If any of the selected assets in the stack produce one of the errors identified on the Upload Assets page, none of the assets in the stack are uploaded. You must correct the erroneous file(s) and upload the stack once all the items in the stack are valid file types.