I had the same error. The term TB refers to "Text Box" and no selector is referring to the fact that there is no option for a response.
Qualtrics article says this: "The Selector describes what interface the respondent uses to make their response to the question. These range from things like "MAVR", "TE", "Likert", "SAVR", "TB", and more. These abbreviations stand for "Multiple Answer Vertical", "Text Entry", "Likert", "Single Answer Vertical", "Text-Box", etc. ""
So, put simply, you've accidentally selected the wrong selector type for a question and there's no way for a survey taker to select a response!
I resolved my error by going through my survey in preview mode to determine when the error would arise. Once I found out what block the error was in, I found out that I had a Question without a response option that was intended to be a text descriptor.