SAP Message VAL602 - More than one book value exists for the position on &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 at &V1&
.
Currently there are several entries as at.

System Response
The valuation is not carried out.

Procedure
Define one book value for the position as at &V1& .