UoM Code randomly comes up blank on sales docs

Hello all,

Here's an issue I've been running into with a client's database.  They are on SAP Business One 9.0 PL07:

The UoM Code column on sales documents is randomly showing up blank for certain items, but there's not pattern to which ones are blank.  If the UoM Code is blank on a sales document, it won't let you add the document, so our client keeps having to remove the row, then reenter it and the UoM code populates fine.  Some documents populate the UoM code without any problem, others have items where the UoM code is randomly blank.

I've scoured the SAP B1 notes and the forums, but I'm not finding anything that tells me why items would have the UoM code missing at random on a sales document.

Any help or feed back is appreciated.

Thanks

Glen