Personnel number & could not be locked

What causes this issue?

The personnel number in question was locked by another system activity.
This could have been master data maintenance, for example.

System Response

The payroll results for this personnel number could not be converted.

How to fix this error?

During the conversion run, no activities that cause personnel numbers
to be locked should be performed in the system. The conversion
H99U_CONVERSION_46C must be restarted for the personnel number(s)
affected.

Procedure for System Administrators

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.