ttysrv: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/sbin/ttysrv - from package: remote-tty

You may install the required package with command apt-get install {package}
Error in other languages:
ttysrv: bevel nie gevind nie
ttysrv: comandă negăsită
ttysrv: comando não encontrado
ttysrv: commande introuvable
ttysrv: command not found
ttysrv: käsku ei ole
ttysrv: không tìm thấy lệnh
ttysrv: komanda nerasta
ttysrv: Kommando nicht gefunden.
ttysrv: kommandot finns inte
ttysrv: komut yok
ttysrv: nie znaleziono polecenia
ttysrv: níor aimsíodh an t-ordú
ttysrv: no se encontró la orden
ttysrv: no s'ha trobat l'ordre
ttysrv: opdracht niet gevonden
ttysrv: parancs nem található
ttysrv: perintah tidak ditemukan
ttysrv: príkaz nenájdený
ttysrv: příkaz nenalezen
ttysrv: команда не найдена
ttysrv: командата не е открита
ttysrv: 命令找不到
ttysrv: コマンドが見つかりません