What causes this issue?

You made the business area a required entry field in the screen layout
control or you want business area balance sheets in company code &V1&.
Therefore, every asset has to be explicitly assigned to a business
area.
You did not specify a business area.

System Response

The asset cannot be saved without a business area.

How to fix this error?

Enter the business area or another additional account assignment (such
as cost center, responsible cost center, internal order or maintenance
order) from which the business area could be determined.

Error message extract from SAP system. Copyright SAP SE.