Error: Invoice contains progress bills that have been relieved on a later invoice

Scenario

You may get the following error message when opening an invoice.
Error message
Invoice contains progress bills that have been relieved on a later invoice

Cause

This means that the invoice you're opening has progress billing that has already been relieved. It's typical for this message to display if you intended to relieve the invoice. If you didn't intend to relieve the invoice or to open the invoice, you'll need to clear this message.
For example, let's say invoice 1 is a progress bill. After creating invoice 1, you create invoice 2 and relieve invoice 1. If you go to open invoice 1, you'll receive the message. To open invoice 1, you'll need to either delete invoice 2 or open invoice 2 and unbill the amounts used to relieve invoice 1.
Invoice 1 is referred to as the progress bill. Invoice 2 is referred to as the final bill in the following resolution.

Solution 1: Delete the final bill

First, you'll need to find the final bill. There may be more than 1 invoice involved if the progress bill was relieved in multiple parts rather than on a single invoice.
To figure out which bill is the final bill, expand each invoice to display the time entries involved. The relieved progress amounts display as negative WIP.
  1. Mark the checkbox for the final bill.
  2. Right-click and select
    Delete Selected
    .
  3. Select
    Yes
    to confirm the bill to delete.

Solution 2: Unbill the final bill

First, you'll need to find the final bill. There may be more than 1 invoice involved if the progress bill was relieved in multiple parts rather than on a single invoice.
To figure out which bill is the final bill, expand each invoice to display the time entries involved. The relieved progress amounts display as negative WIP.
  1. Mark the checkbox for the final bill.
  2. Right-click and select
    Open Selected
    .
  3. Select the
    Time & Expense
    tab.
  4. Right-click and select
    Unbill Selected
    . The entry will disappear.
  5. Repeat these steps for all entries used to relieve the progress amount.