Hi Again.
I found the way to fix it.
Replace this lines
in plugins.conf v7
replace these lines:
plugin=1|1|Sega Genesis|genplusgx,wiimednafen-mod3|/genplus/roms/MD|gen,md,zip,bin|Sega_Genesis.png
plugin=1|1|Sega MasterSystem|genplusgx,wiimednafen-mod3|/genplus/roms/MS|sms,zip,bin|Sega_MasterSystem.png
plugin=1|1|SG 1000|genplusgx|/genplus/roms/SG|sg,zip,bin|Sega_SG-1000.png
with these:
plugin=1|1|Sega Genesis|genplusgx,wiimed|/genplus/roms/MD|gen,md,zip,bin|Sega_Genesis.png
plugin=1|1|Sega MasterSystem|genplusgx,wiimed|/genplus/roms/MS|sms,zip,bin|Sega_MasterSystem.png
plugin=1|1|SG 1000|genplusgx,wiimed|/genplus/roms/SG|sg,zip,bin|Sega_SG-1000.png
this could be v8 ;-)
Thanks again to stfour and abz for this great job !