ok so we figured out more of what's going on. When I enter multiple entry lines on an invoice the total at the bottom matches my total on the invoice. When I go to post the invoice I get the error message. If I print off an Invoice Batch Report for that invoice some of the lines I have entered have disappeared.
We then have to do a back up, reenter the lines that are missing and then regenerate. We aren't sure why these entries are disappearing.