SAP Message WS418 - An internal error occurred (see long text)

Diagnosis
An internal error occurred as the system read a document from thearchive.

System Response
The document was not read. Processing cannot continue.

Procedure
INCLUDE ISR_VERWALTUNG

Procedure for System Administration
Contact SAP. The error relates to function module "wlf_generate_index".The system expects a header document when it reads a data record usingfunction module "archive_get_next_record".