Hi Lionel,
It appears to work fine for me, I can capture email attachments from an email and save it under it's original name without errors. It's strange that it tries replacing the accents by "?" (which is invalid in a Windows file name, and is the reason why you get the error), but I find the whole string "=?UTF-8?Q?fichier_factures_ao=C3=BBt_201?= =?UTF-8?Q?7=2Epdf?=" to be very strange. Are you saving the file with one of the PlanetPress system variables (such as %o), or are you using another method to get a file name? Perhaps the problem is there.
Regards,
Raphaël Lalonde-Lefebvre