In that same Logs folder, look for a file called CustomContentObjects.txt. Open it in Notepad, then use the Search function (Ctrl+F) to find the word Singer. I'm guessing that the career is called "Singer" or something similar. It's erroring as "Adult - Singer", which simply means that it's not the teen or elder career, but the adult career as a Singer. Once you find the line that has "Singer" in it, it should hopefully indicate what type of custom content it is and where it is located. Take note of the location and find the file, then remove it.

Unfortunately the error log doesn't help us find the file, but your CC listing should help you locate it.