I think the answer to this question related with the one you give to me in a different thread: view rights control access to content and metadata, but not to document references. Somehow, guest users don’t having “view” any more because I set this permission to me, are still able to see that there are two attachments in Sandbox, although they are not able to see their properties.
In any case, that doesn’t explain why I’m not able to delete the attachment I uploaded. I was trying to delete it by using the account, the only one on that XWiki now, I used to upload it.
Thanks!