There are several possible causes of this problem. Often it is temporary and will be resolved by just trying again. To try again close the classroom login window, go back to "My Account" and click "Go to Class" again. The login will be reset and a new login attempt started.
You can not login with your Franklin Virtual High School login to this screen:
If you are still unable to enter your Classroom at this point, contact Student Services at 888-990-3847 , click on Live Chat or post a help desk desk ticket.