Maintain settings in Customizing for free assignment of components

What causes this issue?

You want to allocate components that do not exist in your object
structure to your task list. In detail these are:
for equipment task lists: equipment or assembly BOM
for functional location task lists: functional location or assembly BOM

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

for general maintenance task lists: BOM for assembly in task list header

System Response

Task list settings must be maintained before allocating any materials.

How to fix this error?

Maintain the entry "BOM Usage" in the implementation guidelines for
Plant Maintenance under "Planning -> Task lists -> Control data ->
Settings for free material allocation". This BOM usage should correspond
to that of your maintenance bills of material.

Error message extract from SAP system. Copyright SAP SE.