Hello there, @DGS1.

I appreciate you performing the recommendation of my colleague. Let's try some more steps to surpass the "Unable to add the item to list" message.

Aside from the Verify/Rebuild tool, re-sorting your list can also fix data damage on your company file. Please keep in mind that you'll need to close and re-open your company file after re-sorting a specific list.

For Customer list:

1. Open the Customer Center.
2. On top left menu, click Edit.
3. Select Re-sort List.
4. Click OK on the Are you sure you want to return this list to its original order? prompt.

For Master Name List:

1. Choose the Banking menu.
2. Select Write Checks.
3. Place the cursor in the Pay to the Order Of field.
4. On your keyboard, press and hold the Command / Apple key, and press the L key to open the Master Name list.
5. Ensure All Names is selected at the bottom of the list (or in earlier versions of QuickBooks, Include Inactive should be displayed at the bottom of the list).
6. On top left menu, click Edit.
7. Select Re-sort List.
8. Click OK on the Are you sure you want to return this list to its original order? prompt.

For Chart of Accounts:

1. Go to the Lists menu.
2. Select Chart of Accounts.
3. Ensure All Accounts (or Include Inactive in earlier versions) is selected at the bottom of the list.
4. On top left menu, click Edit.
5. Select Re-sort List.
6. Click OK on the Are you sure you want to return this list to its original order? prompt.

For Item and Class list:

1. Open the Item or Class list.
2. On top left menu, click Edit.
3. Select Re-sort List.
4. Click OK on the Are you sure you want to return this list to its original order? prompt.

For your reference, you can check this link: Re-sort lists for QB Mac.

If you get the same result, I recommend reaching out to our phone agents. They can have a screen sharing session with you to take a closer look of your issue.

1. Go to https://help.quickbooks.intuit.com/en_US/contact
2. Select your product.
3. Select your QuickBooks version.
4. Select a topic.
5. Click on the Get Phone Number button.

Let me know how it goes or if you have any follow-up questions. I'll be here if you need further assistance. Take care always.