Thank you for trying the steps provided by my colleague, @JenniferM91. 

Since you're still having an error after clearing your browser's cache, I suggest contacting our Customer Support. They have the tools to get into your account and check why you're having this error and help you resolve it. 

Here's how to contact the QuickBooks Online Customer Support team. 

Let me know if there’s anything that I can help with your account. I’m always here to assist.