@daxtsu I believe
@angelhp is attempting to report the MAME cores as nonworking rather than nonpresent and something is being lost in the translation. The user reports after the "not found" remark that they get a black screen launching these cores. I get similar results here, with the 3dsxs for all of the "XML-required" cores (FBA Alpha, MAME 2000, MAME 2003) locking up before RGUI is able to launch. The bottom screen log locks up after the warning about calculating refresh rates, etc.
A handful of users have been reporting this issue for a week or so, I'm unsure as to whether other users are not experiencing the issue at all or simply haven't encountered it due to not running said cores. I've only just updated to the current nightly from the one I was using (about two weeks old) so I'm not sure when exactly this started.