In the template.xml, you should declare the parent of your template.
For example, if your template extends the "default" template :
<?xml version="1.0" encoding="UTF-8"?>
<template xmlns="http://thelia.net/schema/dic/template"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://thelia.net/schema/dic/template http://thelia.net/schema/dic/template/template-1_0.xsd">
<descriptive locale="en">
<title>My template</title>
</descriptive>
<parent>default</parent> <!-- declare the parent here -->
<languages>
<language>en_US</language>
</languages>
<version>1.0.0</version>
...
</template>
