SAP Message 6P014 - Requirement already exists and can be changed after pressing enter

Diagnosis
A requirement already exists witht the corresponding features for theentered material number.

Procedure
After pressing "Enter", the available requirement will be displayed forprocessing.
The entered data (quantity, date, and so on) are ignored. If thealready existing requirement has several dates, then the total quantityis displayed. Otherwise, the quantity and the date of the availablerequirement is displayed.