What version/release date of imagevue are you using? The "login" directly from the gallery was something temporary we had some time ago that we removed ... You can login by going directly to your gallery admin:
yourgallery/imagevue/
You should read through the quickstart guide:
https://www.photo.gallery/v2docs/quickstart/
Sounds like you have successfully uploaded images through FTP, but you need to create thumbnails for them from the admin.