Indent/Outdent of activities in MS Project

Member for

19 years 11 months

It looks self explanatory, doesn’t it?

Look at the task that you are about to make into a heading by indenting the other tasks under it.

It will have predecessors and/or successors.

Remove them.

Now indent the other tasks and it will be ok.

You cannot have a task whose predecessor or successor is its own heading. It would be like linking a task to itself.