xls2csv: 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 CentOS possible default full paths are:

/usr/bin/xls2csv - from package: catdoc

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/xls2csv - from package: catdoc
/usr/lib/R/site-library/gdata/bin/xls2csv - from package: r-cran-gdata

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

Error in other languages:
xls2csv: bevel nie gevind nie
xls2csv: comandă negăsită
xls2csv: comando não encontrado
xls2csv: commande introuvable
xls2csv: command not found
xls2csv: käsku ei ole
xls2csv: không tìm thấy lệnh
xls2csv: komanda nerasta
xls2csv: Kommando nicht gefunden.
xls2csv: kommandot finns inte
xls2csv: komut yok
xls2csv: nie znaleziono polecenia
xls2csv: níor aimsíodh an t-ordú
xls2csv: no se encontró la orden
xls2csv: no s'ha trobat l'ordre
xls2csv: opdracht niet gevonden
xls2csv: parancs nem található
xls2csv: perintah tidak ditemukan
xls2csv: príkaz nenájdený
xls2csv: příkaz nenalezen
xls2csv: команда не найдена
xls2csv: командата не е открита
xls2csv: 命令找不到
xls2csv: コマンドが見つかりません