mimetex: 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/x86_64-linux-gnu/kadu/plugins/bin/mime_tex/mimetex - from package: kadu-mime-tex
/usr/bin/mimetex - from package: mimetex

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

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