After activating material ledger, live data must be converted

What causes this issue?

You have indicated that the material ledger is to be <LS>activated
</>for one or more valuation areas.
After you activate the material ledger, you must convert the data for
these valuation areas to your <LS>live system</>. This ensures
consistency of the valuation data and the material ledger is flagged
internally as being <LS>in production</>.

System Response

You can only start up production in these valuation areas in Materials
Management once the data has been converted after activation of the
Material Ledger.

How to fix this error?

IF &[SWITCH]S4H_DOCU_ON_PREMISE& = 'X'.
Decide the valuation areas for which you wish to activate the Material
Ledger.
Print out this system message.
Save your Customizing settings.
Convert the data for the Material Ledger.
You have two options:
You activate the Material Ledger in a system that does not contain any
production data and transport the Customizing settings to your
production system.
You must ensure that the data is converted for the Material Ledger in
the production system before you start work with Materials Management.
You activate the Material Ledger in a system containing production
data. Immediately after activating the Material Ledger, you must convert
the data for production start-up.
Choose <LS>Accounting -> Controlling -> Actual costing/Material ledger
-> Utilities -> Production startup</>.
ENDIF.
IF &[SWITCH]S4H_DOCU_CLOUD& = 'X'.
Contact your system administrator.
ENDIF.

Error message extract from SAP system. Copyright SAP SE.