You are trying to delete a program and there is nothing inside that program, no folder or assets or anything. [Here is a DOC on deleting a program]
When you attempt to delete the program it says it is in use. (See Screenshot)
The usual cause of the program was that at one point a Smart Campaign may have referenced that program or a Smart List using the filter "Member of Program"
If you have moved the program to the Archive folder, the program will no longer be searchable in the dropdown for the filter. (This can be seen in this Related DOC)
However, any references to the program will still remain.
You can view where the program is being used by changing the view of the program. (See screenshot) This is also mentioned in the Delete a Program Article
Clicking on the Smart Campaign or Smart List, you can then remove the reference and then continue to delete the program.