Thanks for actively responding, @knapiks. At the moment, QuickBooks doesn't have a list of invalid characters. 

QuickBooks follows the OFX Consortium's specific Offx guidelines. If a financial institution fails to meet these, QuickBooks won't be able to import the .qbo file.

At this point, I'd suggest you contact your financial institution as this could be a formatting issue that they need to correct. Web Connect banking companies and financial institutions know how to deal with this kind of problem.

Additionally, it's best to get your Bank Log files before contacting your bank to help them find the issue or error.

You can also follow the steps to review the Web Connect file for errors under Next Steps: Advance troubleshooting outlined in this help article: Fix Web Connect import errors. 

Feel free to visit again if you need anything else. We'll be here to help you more.