How to block particular condition type not being posted

Hi,

We don't want a particular condition type ( customized & accruel ) to be posted into accounting when creating a billing. That condition type is deleted and after that this is how it works now.

1. When a billing is cretaed from a new sale order ( which does not have that condition type ) it works fine.

2. When a billing is created from a sale order which refers to the old sale order which in turn has this condition type, then this conditon type is posted into accounting.

Can some one help in this issue so that I want to block this condition type being get posted in accounting. Is there any Userexit or can it be done with other options. I am an ABAPer, please give specific answer.