Total Float bar didn’t display a red color

Ask,
1. Check the relationships of the total float (0) activities there may me an open end wihtout a relationship hence link them accordingly.
2. If the relationships are linked properly then you see the relationship ie, link of all the activites which are showing red colour and know the base link ie major link and now when you link this base link with the logic for the non red bar activities in predecessor or successor for sure you will get them in red bar.
3. If all the total float (0) activites are linked with a Milestone then they will display a red color bar however check for the relationships with the key link.
Hope the Answer.