gapi3-fixup: 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/gapi3-fixup - from package: gtk-sharp3-gapi

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

Error in other languages:
gapi3-fixup: bevel nie gevind nie
gapi3-fixup: comandă negăsită
gapi3-fixup: comando não encontrado
gapi3-fixup: commande introuvable
gapi3-fixup: command not found
gapi3-fixup: käsku ei ole
gapi3-fixup: không tìm thấy lệnh
gapi3-fixup: komanda nerasta
gapi3-fixup: Kommando nicht gefunden.
gapi3-fixup: kommandot finns inte
gapi3-fixup: komut yok
gapi3-fixup: nie znaleziono polecenia
gapi3-fixup: níor aimsíodh an t-ordú
gapi3-fixup: no se encontró la orden
gapi3-fixup: no s'ha trobat l'ordre
gapi3-fixup: opdracht niet gevonden
gapi3-fixup: parancs nem található
gapi3-fixup: perintah tidak ditemukan
gapi3-fixup: príkaz nenájdený
gapi3-fixup: příkaz nenalezen
gapi3-fixup: команда не найдена
gapi3-fixup: командата не е открита
gapi3-fixup: 命令找不到
gapi3-fixup: コマンドが見つかりません