I'm sorry to hear that you're having trouble accessing your store. I have a few questions to help troubleshoot this further:
Does this error appear after successfully logging in?
If no, are you using the correct email and/or password for your store?
Is your store appearing online when you enter the URL in your browser?
Peter | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog