variant_comp: 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/lib/seqan/bin/variant_comp - from package: seqan-apps

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

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