horde-import-squirrelmail-prefs: 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 CentOS possible default full paths are:

/usr/bin/horde-import-squirrelmail-prefs - 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-import-squirrelmail-prefs - from package: php-horde

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

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