Magento 2.2.0 upgrade, error attribute type is not allowed

Those lines are most likely ones in your layout XMLs:

Element 'block', attribute 'type': The attribute 'type' is not allowed.
Line: 776

Element 'block', attribute 'type': The attribute 'type' is not allowed.
Line: 783

Element 'block', attribute 'type': The attribute 'type' is not allowed.
Line: 816

Most likely in layout XMLs you have declarations like

<block type="..."

Which does not correspond to lib/internal/Magento/Framework/View/Layout/etc/elements.xsd and need to be replaced to

<block class="..."