Hi ZenunJ,
Here is an article for your reference: Manage large lists and libraries in SharePoint
The error message may not be related with the number of the items.
To better understand your situation and provide help for you, please help confirm some information:
- Does the issue happen with other document library?
- The issue happens in the folder "Financial Document Library", if you create a test folder in "FinancialSystem", will the error message appear?
Best Regards,
Gloria