The "Interactive Schedule.apx" Add-On file should be stored in the "Add-Ons" folder as the message describes. This Add-On should be located in the "Standard" sub-folder of the "Add-Ons" folder.
You may need to re-install the ArchiCAD application, this should fix the issue.
David Larrew, AIA, GDLA, GSRC
Architectural Technology Specialist
a r c h i S O L U T I O N S
WIN7-10/ OSX 10.15.7
AC 5.1-25 USA