fitscheck: 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/fitscheck - from package: pyfits

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

On Debian possible default full paths are:

/usr/bin/fitscheck - from package: pyfits-utils

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

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