gcm-viewer: 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/gcm-viewer - from package: gnome-color-manager

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

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