SAP Message VAL609 - The implicit index was set to 1

Diagnosis
You wish to carry out a manual valuation for the position on &V1&. Toenable this, book values must have been defined in the system as atV1.
The system determines an implicit index from the book value clean andbook value in position currency. This is not possible in this casesince at least one of the two book values is 0.

System Response
The implicit index was set to 1.