Yes, I don’t think you can use backups created by current 2.0 with 1.8 Legacy anymore. The paths of 2.0 and 1.8 Legacy diverged approx. 1 month ago with this update for 2.0:
See here as well:
However, if your intention was to stay on 2.0 but were forced to revert to 1.8 Legacy because 2.0 was not playing music, this is a different issue that still should be resolved, but I think we have to wait for @noris for this