I am pretty sure the message 'DO NOT BOARD - CONTACT US TSA/CBP' means 'DO NOT BOARD - CONTACT US TSA/CBP.'
It might be an immigration issue, and they were not willing to let you enter into the US anymore, despite your B1 visa. Has your life situation changeschanged lately?
Or it can be a safety issue, and they thought that for whatever reason you are a risk for air transportation. That is, your name is in the no fly list.