When you using the reorder icon, if you want to move a project to a new program(here we use the example above: MAX Program, which is a new platform that with no project under it), you should ensure the program(MAX Program) has at least one project under it. The reason why you cannot move the project under a new program is that there is nothing under the new program, and OnePlan think you are going to move the project(as a program) under the new program which not match with what the hierarchy structure is. 

 
Tips:

1.     When you create a new Program level, use the hamburger menu (reorganize feature) to move one project under the Program level.

2.     Then you can use reorder icon on the top banner to move other projects which you want to include in that Program.