Not Working for WoW Classic Era. Please update it, thank you very much.

Still works as of v1.4.2. Make sure you're using the latest classic version and not the TBC version. Also that there's no other unitframe addons causing conflicts.

As a last resort, you can reset all of ClassicCastbars to default by running this script ingame twice:
/run ClassicCastbarsDB=nil;ClassicCastbarsCharDB=nil;EnableAddOn("ClassicCastbars");EnableAddOn("ClassicCastbars_Options")ReloadUI();