OKB9 - ProfitCentre/Cost Centre

I have done the OKB9 settings as follows for cost element posting GBB-VQP (Quality Inspection):

CO. code : 1200

Cost Elemetn : 405987

Then Acc. Assignment Detail : 3 (Profit Centre Mandatory)

(No cost centre is assigned here)

In the "Detail per profit Centre", I have assigned different profit centres and the relevant cost centre for posting. However, system is still giving error message that "CO Account assignment is missing". Have I done it properly ? Should I give a default cost centre in the opening screen itself ?