That's probably because you've restored XenoAmp database instead of refreshing it! Note that some ROMs have different mount points for sdcard and external sdcard. That happens i.e. between CM based ROMs and AOKP ROMs. If you restore old XenoAmp database all paths will point to non-existent places and you won't be able to play anything. Just do a full refresh (Refresh metatata from "where's my musuic" in preferences).