I have 3 machines to backup, that have been configured for backup in the same way (all 3 are linux servers backed up by rsyncd).

In the CGI interface, only 2 out of them appear in the small scrollable list where I can choose the host to survey. However, if I try to go on the status page of the third one, I get

Note: $ENV{REMOTE_USER} is not set, which could mean there is an installation problem. BackupPC_Admin expects Apache to authenticate the user and pass their user name into this script as the REMOTE_USER environment variable. See the documentation.

How can REMOTE_USER be set for two machines, but not for the third? I'm at a loss...

Thanks for any hint!