Microsoft.Build.Tasks.v12.0.dll: 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/Microsoft.Build.Tasks.v12.0.dll - from package: mono-xbuild

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

Error in other languages:
Microsoft.Build.Tasks.v12.0.dll: bevel nie gevind nie
Microsoft.Build.Tasks.v12.0.dll: comandă negăsită
Microsoft.Build.Tasks.v12.0.dll: comando não encontrado
Microsoft.Build.Tasks.v12.0.dll: commande introuvable
Microsoft.Build.Tasks.v12.0.dll: command not found
Microsoft.Build.Tasks.v12.0.dll: käsku ei ole
Microsoft.Build.Tasks.v12.0.dll: không tìm thấy lệnh
Microsoft.Build.Tasks.v12.0.dll: komanda nerasta
Microsoft.Build.Tasks.v12.0.dll: Kommando nicht gefunden.
Microsoft.Build.Tasks.v12.0.dll: kommandot finns inte
Microsoft.Build.Tasks.v12.0.dll: komut yok
Microsoft.Build.Tasks.v12.0.dll: nie znaleziono polecenia
Microsoft.Build.Tasks.v12.0.dll: níor aimsíodh an t-ordú
Microsoft.Build.Tasks.v12.0.dll: no se encontró la orden
Microsoft.Build.Tasks.v12.0.dll: no s'ha trobat l'ordre
Microsoft.Build.Tasks.v12.0.dll: opdracht niet gevonden
Microsoft.Build.Tasks.v12.0.dll: parancs nem található
Microsoft.Build.Tasks.v12.0.dll: perintah tidak ditemukan
Microsoft.Build.Tasks.v12.0.dll: príkaz nenájdený
Microsoft.Build.Tasks.v12.0.dll: příkaz nenalezen
Microsoft.Build.Tasks.v12.0.dll: команда не найдена
Microsoft.Build.Tasks.v12.0.dll: командата не е открита
Microsoft.Build.Tasks.v12.0.dll: 命令找不到
Microsoft.Build.Tasks.v12.0.dll: コマンドが見つかりません