Error during background generation of cost collectors - refer to spool

What causes this issue?

You are attempting to generate cost collectors in the background. An
error occurred during this process.
All selected settlement units have been checked, but no cost collectors
were generated or deleted.

System Response

The system only allows changes in the background when all checks are
successful.

How to fix this error?

Look at the <ZH>spool</> file for your job, which contains the error
messages.
Change the faulty settlement units online. If necessary, exclude faulty
settlement units from background processing by using a variant.

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.