When you are in Process Industry environment the Bill of Material is maintained in a recipe in transaction C202. If you try to maintain it directly through CS02 the system will give you the error: “BOM can only be extended via Master Recipe”.
In some cases it may be necessary to still maintain the BOM in CS02 even though you are in a process environment. To bypass the error where it is not possible to create a BOM once a Master Recipe was maintained for a material implement SAP note 651282. This will allow you to change the status of the message to either warning, error or no message at all.