Hi
You should analyse how the der rule is written and the reason of failure
If you did not maintain the rule values in KEDE, just maintain them and it wil be done
If it is not able to derive a char as per the der rule, you should check what parameters (chars) are needed to derive it and whether they are available or not
If the above does not help, do paste a screen shot of your der rule and what data you entered in your sales order
You can also debug your der rules using the func module KEDR_COPA_DERIVE.. How to use this FM is written inside the FM itself
Br, Ajay M