This is a backstage information, so you might be confused, but this is the correct way to explain to a expert :)

If someone has as in this sample made it possibel for your BC to have 3 decimals, in some places, a BC modfication, then not all numbers has 3 decimals or 4 or.., then our check give you a fail, you cant send the document as numbers dont match

In the case below, 

689.83 is different from 698.832, so you get a error on trying to send