If you are seeing this error, it means that your album has already been imported into at least one of your websites. There are currently three workarounds to get this album on your desired website.
1. Create a copy of the album in Lightroom and share the copy to Adobe Portfolio.
2. Change your default website to the website you wish to import the album to. More on how to change your default website here. Then share the album from the Lightroom platform to Adobe Portfolio.
3. Delete the album on all sites and attempt to import again.