When accessing LabTutor Client or LabTutor Server, I get an 'error 503 - service unavailable' error message. How do I resolve this?

A 503 error is symptomatic of Port 80 (a Port that the LabTutor Server needs to use) being blocked by Windows' Internet Information Services (IIS).
servlet.ImageServer?id=015w0000003Ohx0&oid=00D20000000HncM 
This issue can be confirmed by running the ADInstruments' LabTutor Server Installation Advisor - IIS will show as Port 80 being used by 'System'. This often occurs on Windows 10 Machines where IIS is enabled by default.
To resolve this issue, follow these steps to disable IIS on your system:
- Open your system's Control Panel:
On Windows 7: Start | Control Panel
On Windows 8: Mouse to the right of your screen to open the Charms Bar | Settings | Control Panel
On Windows 10: Right-click the Start Button | Control Panel
-
Go to Programs | Turn Windows Features on or off
-
Locate Internet Information Services from the list and uncheck the box to disable it (this may require a restart of your machine):
servlet.ImageServer?id=015w0000003OhwM&oid=00D20000000HncM

-
Restart the LabTutor Server Service (Ctrl + R | Type 'services.msc' | Select LabTutor Server Service | Click 'Restart')
Note that IIS can sometimes be re-enabled if the LabTutor Server machine is restarted.

---
Note that this issue can also present as a 404 error instead of a 503 error.