SAP Message VAL608 - The implicit foreign exchange rate 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 foreign exchange rate from the bookvalues in position and valuation currency. This is not possible in thiscase since at least one of the two book values is 0.

System Response
The implicit foreign exchange rate was set to 1.