You may experience this error when you use "Site wizard" or "Add New Portal" in DNN 4.5.3, 4.5.4 or 4.5.5

template is not a valid Portal Template File

Validation Results
The element 'tab' has invalid child element 'issecure'. List of possible elements expected: 'panes, parent, tabtype'.

Here is the fix for it:

1. Download the file
2. Unzip the file
3. Upload to "\admin\Portal" overwrite "portal.template.xsd"
4. Re-Export using "Host/Portals/Export Portal Template"
5. This file works for DNN Version 4.5.5