qucsconv: 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/qucsconv - from package: qucs

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

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