ICSharpCode.Decompiler.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/monodevelop/bin/ICSharpCode.Decompiler.dll - from package: monodevelop

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

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