SAP Safari

Today we had an account determination issue that made the day interesting... The problem was that the invoice document was not posted to accounts because of the 'Account Determination Error'. When there is an Account Determination Error, the first place to look at is the 'Account Assignment' field in the Customer and Material Masters, whether anything had been changed? Because if a smooth working system suddenly stops working the first casualty could be the master Data. When I checked that there was no change in the Customer Master. However there was a change in the Material Master Data that it was set for deletion. I was tempted to buy that reason but I realised that the efforts to post to Accounts was done much ahead of the deletion flag indication being set. However that was also a learning point - when you can't process an article that was marked for deletion in Sales Order itself, there is no way that the article came via Sales Order.