tcpdump2xplot: command not found

Have You tried accessing the binary with the full path?

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/tcpdump2xplot - from package: xplot-xplot.org

You may install the required package with command apt-get install {package}
Error in other languages:
tcpdump2xplot: bevel nie gevind nie
tcpdump2xplot: comandă negăsită
tcpdump2xplot: comando não encontrado
tcpdump2xplot: commande introuvable
tcpdump2xplot: command not found
tcpdump2xplot: käsku ei ole
tcpdump2xplot: không tìm thấy lệnh
tcpdump2xplot: komanda nerasta
tcpdump2xplot: Kommando nicht gefunden.
tcpdump2xplot: kommandot finns inte
tcpdump2xplot: komut yok
tcpdump2xplot: nie znaleziono polecenia
tcpdump2xplot: níor aimsíodh an t-ordú
tcpdump2xplot: no se encontró la orden
tcpdump2xplot: no s'ha trobat l'ordre
tcpdump2xplot: opdracht niet gevonden
tcpdump2xplot: parancs nem található
tcpdump2xplot: perintah tidak ditemukan
tcpdump2xplot: príkaz nenájdený
tcpdump2xplot: příkaz nenalezen
tcpdump2xplot: команда не найдена
tcpdump2xplot: командата не е открита
tcpdump2xplot: 命令找不到
tcpdump2xplot: コマンドが見つかりません