1. Windows Protected PC message box appears with 'Do Not Run' - what do I do? 

When you have downloaded the CalDAV plugin from Source Forge if you see the following window appear:

Please click on 'More Info' as shown below:

This will show a 'Run anyway' button which you will need to click on as shown below: 

The CalDAV plugin will then be downloaded.

2. Error Message 'Response status code does not indicate success 401 (Unauthorised) message' window pops up when I clicked on 'Test or discover settings' 

If when you click on the 'Test or discover settings' button you see an error message (as shown in the screenshots below)

This will be likely to you either having incorrectly entered your calendar ICAL or having pasted in your calendar ICAL into the DAV Url: field. 

Please make sure you manually type your ICAL address in and not paste this. 

This may also be due to you having mistyped your DAV URL or Username - please make sure you match the case with your icomplete username for instance if your username is lowercase use lowercase.  

If your username has an uppercase first character for example 'Sarah' use an uppercase 'S' as shown in the example screenshot below: