Can we do costing for Group BOM /Phantom BOM by CK11n...as getting error of BOM is invalid when run CK11n for it.....
If the BOM and items are relevant for costing can be used in cost run CK11n.
May be phantom assembly has NO valid BOM. Check costing relevancy indicator is set for components.
Also check that BOM has valid status.
For Phantom item costing please refer SAP note 131733 - Indicator fr relvncy to costng for phantom assembly