maskseq: 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/maskseq - from package: emboss

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

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