Please convert CO data first

What causes this issue?

The last system update contained new CO database tables for transaction
data. To avoid inconsistencies, the existing data must first be
converted to the new tables. Only then can you create new data.

System Response

The desired transaction is currently not possible.

How to fix this error?

Either start the conversion of the CO transaction data or wait until
the conversion is completed.

Error message extract from SAP system. Copyright SAP SE.