With the following fix, you may fix the 80040408 QuickBooks error: Rename the Quickbooks company file to the original one as a first step.

As previously mentioned in the QQube Configuration Tool, you can alter the name of your business file when the company file's name changes. By deleting the business file, you can also change the file's name back to its original one. To rename the server, you need a multi-user version. Try the following fix if you're still having difficulties opening QuickBooks and getting error 80040408. 

Option 2: Set up just one system.

QuickBooks error code 80040408 could be brought on by an unstable configuration in terminal/remote desktop settings.
This happens when numerous users sync to the system via the network.
Instead of syncing with the server and other users, QuickBooks needs to be set up to sync with the system only once.

Solution 3: An Alternative

Try the following procedures if the previously mentioned methods do not work:

• Make sure QuickBooks Quick Start is not chosen by checking.
• The Single User Mode of QuickBooks is not being used by other users.
• The server has to be operational.
• To avoid accessing several company files, the QuickBooks programme does not include a command to open a single company file.

Recommended To Read:-  QuickBooks Enterprise Errors