Not an Astaro problem, but something to be aware of. Windows renames the u2d-sys-7.075.tgz.gpg file to u2d-sys-7.075.tgz.gz
If the user is unaware and tries to upload, it will result in error: Extension not allowed, please upload a file with extension .tgz.gpg
Simply renaming the file back to its original name in Windows explorer prior to uploading to the ASG will solve the problem.