@voljega you were right to the point! I am using a pre-configured recalbox image and the es_systems.cfg was incorrect.
Original version:
<system>
<fullname>Dos (x86)</fullname>
<name>dos</name>
<path>/recalbox/share/roms/dos</path>
<extension>.pc .PC .dos .DOS</extension>
<command>python /usr/lib/python2.7/site-packages/configgen/emulatorlauncher.pyc %CONTROLLERSCONFIG% -system %SYSTEM% -rom %ROM% -emulator %EMULATOR% -core %CORE% -ratio %RATIO% %NETPLAY%</command>
<platform>pc</platform>
<theme>pc</theme>
<emulators/>
</system>
Problematic version:
<system>
<fullname>Dos (x86)</fullname>
<name>dos</name>
<path>/recalbox/share/roms/dos</path>
<extension>.sh .exe .EXE</extension>
<command>python /usr/lib/python2.7/site-packages/configgen/emulatorlauncher.pyc %CONTROLLERSCONFIG% -system %SYSTEM% -rom %ROM% -emulator %EMULATOR% -core %CORE% -ratio %RATIO% %NETPLAY% </command>
<platform>pc</platform>
<theme>dos</theme>
<emulators>
<emulator name="libretro">
<cores>
<core>nxengine</core>
</cores>
</emulator>
</emulators>
</system>
Thanks!!!!
