diffseq: 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/diffseq - from package: emboss

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

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