Can not access any menu options

During the initial setup, I added a few accounts that I didn’t have the login information for. Now, I can not access the menus , because the client is trying to sync, and failing. This puts an error window on top of everything and doesn’t allow me to click on anything else. No human is fast enough to click the error button then click on anything else. Help… (I’m sure it is something simple that I am overlooking…)