Welcome to the Community, @AccountingPro1.
I'd be glad to help you in opening the IIF file.
To avoid any error in opening the .iif file, make sure to not double click it.
When the file association of the .iif file is changed to other applications other than MS Excel this type of error occurs. You can verify the type of file you're opening by doing a right-click and access the properties option.
You can also change the file association of the .iif file to open with MS Excel so you can open the file.
Please feel free to read this article to learn how to import IIF files in QuickBooks Desktop: Export, import, and edit IIF files.
Keep me updated by hitting the Reply button. Enjoy the rest of the week and stay safe!
