Error message KD302

Hello experts,

First of all, I have customize a splitting structure which contains cost elements primary and secondary (all of these are assesment type). So then I execute a plan assesment in order to allocation expenses from indirect cost center to direct cost center. Then I execute the splitting structure and the system reports the error KD302: "Cost Center XXXXX, cost element XXXXX: Splitting is not possible".

I know that if I enter an equivalance number in the transaction kp26 for that cost center, the message is solved but is not correct. Because The value of assesment cost elements have to be allocated in the corresponding activity defined in the splitting structure, not allocated proportionately in all activities therefore the price rate of the activities are wrong.

Do you know any way to solve this (any point of customizing left)? If not, do you know any note OSS to solve it?

Thanks of all in advance.