Error in :Posting keys for account determination

Hi, Gurus,

      please suggest the solution for the following problem.

            we are selling two  types of materials, one is the  product material and the second one is the scrap material.Different type pricing procedures, sale order,delivery and billing types were configured for the same. For CST and VAT   same condition type  :"ZCST - for CST " and  ZVAT - for VAT" were used in both pricing procedure and the standard account keys : MW1 for ZCST and MWS for ZVAT  and  same G/L accounts configured .

.                                                   key combination for the condition types as mentioned below:

.                                                        ZCST:  Country/PlntRegion/Region/TaxCl2Cust/TaxCl.2Mat

                                                         ZVAT: Country/PlntRegion/Region/TaxCl1Cust/TaxCl.Mat

     Now we want to capture  CST and VAT seperately for both the materails.For that two new account keys created and incorporated the same in scrap pricing procedure and  and new  G/Ls created and assigned .Now the system is throwing  following error while while releasing the billing document to accounting document.

Posting keys for account determination for transaction Z48 do not exist

Message no. F5598

here Z48 is the new accounting key created for  the  CST tax.We tried all the possibilities, but system is throwing the same error.

with regards

sam