lp_solve: 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/lp_solve - from package: lpsolve

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

On Debian possible default full paths are:

/usr/bin/lp_solve - from package: lp-solve

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

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