Yeah, that happens sometimes. It's been happening to me a lot. Try asking the charter to convert it on their end if you converted it yourself. And if it still doesn't work, verify with the charter that they're using the latest version of the toolkit. It's really strange - I've had a few songs not show up for the longest time, and just now I restarted steam and started Rocksmith and there they were. Who knows how long they'll be there before they disappear again!