Red dates on the schedule board

Hi all,
Just wondering if anyone has come across an issue within the Resource Scheduling Board.

As you can see on this screen shot we have three days that are in red, now we have no jobs or operations on them dates for this resource. Every time I try and move the top job (after I’ve unlocked the job of course) into them red dates the job removes from the board but if still on my works to list for the resource.

So my questions are

  1. What are the red dates and how can I fix them?
  2. Why does the job remove itself from the board if I schedule a job on them dates?

Thanks in advance.