Let's make sure that you're able to make changes to your expense account, AmyMac.

I have some steps to recommend that can resolved issues when making changes to 1099 accounts. Here's how:

1. Go back to the 1099 Wizard.
2. Proceed to Step 3: Map Accounts.
3. Look for the expense account and temporarily assign it to Box 7.
4. Click Save and close.
5. Reopen the 1099 Wizard and go back to Step 3: Map Accounts.
6. Look for the account and make sure to select Omit these payments from 1099 in the Apply payments to this 1099 box column.
7. Click Save and close.

Once done, go back your Chart of Accounts and check if you can already create a sub-account. 

Keep me posted or add a reply below if you need more help with your expense accounts.