I don't know if this has been posted before - if so I did not find anything on this, so I wanted to pass this on.
I have run into this same occurrence 3 times now. 2 were after upgrading from 4.3 (or prior) to version 4.5. one was on a new 4.5 install where we imported some items. When I first saw it, I called Sage and they did not have any clue what the cause was, so I tracked it down on my own. Perhaps by now they have had this enough to know about it, but here is what I have discovered in case anyone else runs across this too
In sales order users are getting a message ""IS NOT ON FILE"" after putting an item on the order (see screen shot below) the message pops up after they ""leave"" the line. It is item specific. If you see this, you can use DFDM to correct the problem. If you look at the item in DFDM you will find that The field ""PrimaryAPDivisionNo$"" will have ""00"" as the division but the field ""PrimayVendorNo$"" is blank. To fix it, simply edit the division field to be null and that will correct the problem.
Optionally (and the client can do this) is open the item in item maintenance and assign a primary vendor, accept and save the changes. If they don't want to have a primary vendor then bring the item up after saving, and remove the primary vendor and save it again.
I wrote a crystal report (SUPER generic but I attached it anyway) that clients can put on the Sage100 menu and run. the report will show you all the offending items numbers.If you run the report and find there are more than can be manually adjusted It may mean someone has to create a custom routine to clean it up. perhaps Sage has one by now but I have not checked.