xbuild.rsp: 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/mono/xbuild/12.0/bin/xbuild.rsp - from package: mono-xbuild

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

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