convcal: 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/convcal - from package: grace

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

On Debian possible default full paths are:

/usr/bin/convcal - from package: grace

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

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