SSH Error: /bin/bash no such file or directory

[yasser]

Hi

i have two machines, a web server and a back up server.
on the backup server there is a user (the same user exists on both servers) who execute a script to backup the web site and the database with rsync
everything was working fine but suddenly not.
when i try to ssh that user from the backup to the web server: ssh user@webserver i got an error message:
/bin/bash: no such file or directory. connection closed.

the ssh from the other side work well (ssh user@backupserver). i can ssh to other users on the remote server.
No chroot used for ssh.

Any ideas about this?

Thanks everyone.