Malolan is obsolutely right. This error will come only if you have assigned your company code (which in turn is assigned to Accounting code) to more than one valuation area.
If you need parallel valuation areas, then as Gurram has pointed out, you can use TPM_INITIALIZE transaction to initialize your company code for each valuation area.
In the 5 odd implementations I have done none of them used the parallel vlauation area. If you do not want this go to the following step and remove the assignment to multiple valuation area and retain just one.
SPRO - Financial supply chain management - Treasury and risk mgmt - Transaction manager - General settings - Accounting - Organization - Assign accounting codes to valuation areas.
My take from this error is the Parallel valuation area is not initialized .
This is a process which is needed if you are using the paralellel valaution area. Probably you have set it up and now the system expects you to initialize the parallel valuation area so that it can go forward to do postings