slonik_execute_script: command not found

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/bin/slonik_execute_script - from package: slony1-2-bin

You may install the required package with command apt-get install {package}

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