I think I'm on to something..!!!

Tonight.. paranoid.. I copied the data to a back up folder before the integrity check ran. Then DC Integrity Check ran successfully (no errors).

So, then I opened Toolkit, as I do at least once a week, and ran an Item Change.

Then I ran the integrity check again and BINGO... OE Sales Order Detail File Error. So I suspect that when Item Changes are posted with Toolkit, it is creating errors in Sales Orders where those items exist. I know forsure that Toolkit used to change the Item code in the Sales Order successfully so perhaps since the OE upgrade, it's no longer working??