clstr_merge_noorder: 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/clstr_merge_noorder - from package: cd-hit

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

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