To avoid the "Missing or invalid * name" error need to make some changes.

Go to directory: /usr/share/webmin/bacula-backup

In section

$in{'name'} =~ /^[a-z0-9.-_]+$/ Change "a-z0-9" to "A-Za-z0-9"

in files: save_director.cgi save_file.cgi save_storagec.cgi