Backup fails to create directory

My scheduled daily backup worked perfectly for months until last Friday.

Without any apparent reason (excepted regular Virtualmin/Webmin updates), it started failing systematically.

Actually, instead of creating the daily directory in the target server according to the File on server setting (/home/ks312228/backup/%Y%m%d in my case), it seems to creates a binary file of the same name of about 17 k. The upload seems to proceed without any error, reporting a correct backup of each sever until the end of the backup process that lasts the usual duration (25 minutes) but reports the following closing message:

Uploading archive to SSH server ks201220.kimsufi.com .. .. upload failed! root@ks201220.kimsufi.com's password: scp: /home/ks312228/backup/20110531: Not a directory

I have attached - the .info file that is created on the target server at the same time as the archive - the binary file that is created at the place of the archive directory - the backup log (all renamed with a .txt extension)

Thanks for help