mprof-heap-viewer: 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/mprof-heap-viewer - from package: mono-profiler

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

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