Some assets are setup with restrictions to limit who can download and freely use an asset.
If you are unable to download an asset, this is related to the permission level you have for the platform/folder. Users with the Preview permission can only view assets online and are not able to download them.
A user must belong to a group which has a permission higher than Preview to be able to download assets.
Please check with your Main Administrator(s) of the platform, who will be able to verify your platform settings, if this is correct.
*Please note: If the folder has a download approval attached, a user in a group with Preview permission will be able to download an asset, subject to approval.