hi @ DavidStagg ,
There are three points we could share:
1. If you have more than 5 users but not interest to use Enterprise edition, you should consider to use QuickBooks 2019 Premier Accountant edition for 10 users.
2. Please ensure to check your Windows Update and no update is available.
3. You could google to find the file of the missing DLL on internet and copy it into your Windows folder.