SAP Message VAL607 - Negative book values are not allowed for securities

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.
This is a security position for which negative book values have beendefined.

System Response
The valuation is terminated.

Procedure
Define only positive book values for the security positions.