As I commented before MAME 2000 has a weird way to look for the content folder... if the front end does not return a directory it tries to create a folder called (null) in the same path as the emulator. In our case this path is read only and it fails.
Other MAME versions and FBA have a different logic, if the front end does not return the path, they create the files under a folder in the content dir.
As a workaround I will create the nvram externally and add to the emulator partition. That will fix these games expecting to read data from nvram on boot.
If you know how to compile the core for arm you are more than welcome to fix the code... the file is called libretro.c
Other MAME versions and FBA have a different logic, if the front end does not return the path, they create the files under a folder in the content dir.
As a workaround I will create the nvram externally and add to the emulator partition. That will fix these games expecting to read data from nvram on boot.
If you know how to compile the core for arm you are more than welcome to fix the code... the file is called libretro.c