Partner function error

Hi SD experts

I have a customer X , and I created another Y copying X with the same account group.

Customer X shows partner functions SP (Sold to = X) and SH (ship to= X ) among others.

However these functions are not copied into Y and that is good becuase I do not want X as sold to/ship to for Y.

However when I try to create partners SP= Y and SH=Y for customer Y , I get an error : Customer Y is not defined for function SP (table TPAKD)

I checked transaction VOPA for partner function/procedure/account group assignment etc and it seems to be OK, moreover it works for customer X, partner function SP = X and SH =X.

Thanks in advance and any help is appreciated

Anton