s2tc_decompress: 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/s2tc_decompress - from package: libtxc-dxtn-s2tc-bin

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

Error in other languages:
s2tc_decompress: bevel nie gevind nie
s2tc_decompress: comandă negăsită
s2tc_decompress: comando não encontrado
s2tc_decompress: commande introuvable
s2tc_decompress: command not found
s2tc_decompress: käsku ei ole
s2tc_decompress: không tìm thấy lệnh
s2tc_decompress: komanda nerasta
s2tc_decompress: Kommando nicht gefunden.
s2tc_decompress: kommandot finns inte
s2tc_decompress: komut yok
s2tc_decompress: nie znaleziono polecenia
s2tc_decompress: níor aimsíodh an t-ordú
s2tc_decompress: no se encontró la orden
s2tc_decompress: no s'ha trobat l'ordre
s2tc_decompress: opdracht niet gevonden
s2tc_decompress: parancs nem található
s2tc_decompress: perintah tidak ditemukan
s2tc_decompress: príkaz nenájdený
s2tc_decompress: příkaz nenalezen
s2tc_decompress: команда не найдена
s2tc_decompress: командата не е открита
s2tc_decompress: 命令找不到
s2tc_decompress: コマンドが見つかりません