horde-queue-run-tasks: 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

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 CentOS possible default full paths are:

/usr/bin/horde-queue-run-tasks - from package: php-horde-horde

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/horde-queue-run-tasks - from package: php-horde

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