Cause 1:
Authentication error

Resolution 1:
Request that your Global Administrator at the school verify that you have been entered as a user with your work email address as the username and have been assigned the 'Timetabler' role.

1. Open https://timetabling.education
2. Open the Management Portal
3. Go to [1A] Manage Users and search for the user. Add the user if they do not exist
4. Select the user and from the top row click "Role" and tick "Timetabler", save and close

Resolution 2:
The time on your system clock must be accurate to allow communication between our devices. If your clock is out by more than 4-5 seconds, you will be unable to sign in using V10.

1. Open V10, located at the bottom middle of the Welcome page, if the sign out hyperlink is available, click Sign out and close V10.  If it is not available, close V10
2. Open Settings
3. Click on Time & Language
4. Click on Date & time
5. Set the time automatically to "ON"
6. Under “Synchronise your clock,” click the Sync now button
7. Restart your machine (this step is required)

Additional information
How to Check Windows Time Sync Status (w32tm /query /status)
How to Resync the System Clock for domain-joined or Intune-managed devices

Cause 2
The registry is missing required information

Resolution 3:  

1. Close V10
2. Download this zip folder https://timetablingmainsite.blob.core.windows.net/files/TDSURLs.zip
3. Right-click to extract the contents, then double-click the extracted file
4. Click Yes and OK to the messages that will appear about adding content to your registry
5. Open V10 and attempt the activation