As we have never used the module before, old historic data exists that needs to be cleared down and archived. Unfortunately, it is not quite apparent on how to do this Can you please help?.
I think it ties in with the VAT Tax report. This marks transactions as posted. You would need to run a report up to a certain date, and post it.
Do some testing on a test system on that to see what results you get. Erp.TaxTran table on a BAQ, checking the Posted bit.