I have the same system in my car (Clio IV) and the navigation system looks like igo/primo/nav'n go/
I would like to update more languages/voices to navi system and the problem is the same as yours.
xxxx.zip <--- name of the file for voice .fbl for map etc..
xxxx.stm <---- textual file, i'have created it with notepad and put just on line (purpose=copy) , if the file exist on the system there will be in .stm file purpose=shadow
xxxx.md5 <---- i have created this file with this program Download the MD5summer
Tried to update with USB and nothing... Without .stm and .md5 i'will get the message (update error).
when I Place an Naviteq map on usb stick into "NaviSync\CONTENT\map" during the toolbox download the toolbox accept it on next startup as preinstalled content I did it with a corresponding .stm (copy) and .md5 file but if I insert this into the media nav it told me License error.
When I edit device_status.ini modified the os_build_version="1.0.0" the server provides an upgrade.lgu
But the media nav would upgrade so is where any other idea to hack