The issue was the usrcheat.dat file indeed. Thank you!! This was driving me crazy as I couldn't find what was causing it. The forwarders now work too after deleting the usrcheat.dat file.For TWLMenu++, try turning off "Update recently played list" in TWLMenu++ Settings. If the issue persists, delete "usrcheat.dat" in "sd:/_nds/TWiLightMenu/extras/".
As for the forwarders, do the games that work in TWLMenu++ also work using forwarders, or is it all forwarders not working?