gcr-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/gcr-viewer - from package: gcr

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

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