Depreciation at main number level should not be changed (Check entry)

What causes this issue?

You are changing the control indicator so that depreciation will be
calculated at main asset number level.

System Response

At the moment the function 'Dep. at MainAssrNo. is not active.
You can make this change. However, it will effect all the assets you
create in the future in this asset class.
Assets already defined will not be effected. If you want them to be,
you must perform a mass change for all the assets.
Instead of changing the control to calculating depreciation at main
asset number, you should consider creating a new asset class.

How to fix this error?

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

Error message extract from SAP system. Copyright SAP SE.