The way the loader\wrapper works as Myself and a couple other users written some a long long time ago was this.
When you run the wrapper its supposed to that the "[Rompath]\Romfile]" variable games passes and then inject it into the NullDC.INI
The INI also may also get edited to launch full screen or other settings but it was trivial.
Once NullDC itself was executed it would then run the game inserted into the INI..
My guess is the issue is with the loader writing to the INI...
I didnt know users were still using NullDC, Makaron or Demul as most have been supereceded my MAME, Refroarch (Reicast, Flycast) and have wonderful performance.
There is another thread here that talks about how to get it up in gameex without the wrapper.