Hi Judith
Usually this message is an indication of a change of sign in information with the bank.If this is not the case, can you try clearing the cache and cookies in the browser (if its chrome that is in the three dots/lines in top right and then history, then history again and then clear browsing data, making sure in the time range you select all time and that cookies and other site data and cached images and files are ticked,then hit on clear data.
Then go back to the Quickbooks and then hit on a different tab which should then sign out the Quickbooks,shut down the browser,reopen and sign back into Quickbooks and when you sign back in if you hit update in the banking section it should connect
If you have any issues just reply back here
Kind regards
Emma