svnauthz-validate: command not found

Have You tried accessing the binary with the full path?

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/debug/usr/bin/svnauthz-validate - from package: subversion-dbg
/usr/bin/svnauthz-validate - from package: subversion

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