That is not a problem of ROM, it is a problem of environment to operate.
When executing EA, FEBuilderGBA defines free space to avoid accidents.
To insert the ORG command, create a temporary file.
Since I can not define the definition of FREESPACE with the option of Core.exe, I need to create a temporary file.
This error occurs if EA(Core.exe) can not access this temporary file for any reason.
I tried a little adjustment with the latest version.
When I passed a temporary file to EA, it was a relative path, so I changed it to absolute path.