those *_ffp.xbe files are created by XBMC. It's because applies a flicker filter patch onto the xbe's on loading.
You can try disabling under Settings (system blade if you're using the mc360 skin) -> Progams.
But still that shouldn't actualy cause any problems. I have no real idea why xboxdash.xbe wont boot anymore, but on another note: why do you need it? It has pretty much no use anymore cause of the alternative dashboards.