doxytag: 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 CentOS possible default full paths are:

/usr/bin/doxytag - from package: doxygen

You may install the required package with command yum install {package}

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