I have errors after the upgrade. You can see error below.
Can anyone help us to fix this error?
1 exception(s): Exception #0 (Magento\Framework\Config\Dom\ValidationException): Element 'block': This element is not expected. Expected is one of ( title, css, link, meta, script, remove, attribute ). Line: 1139
- 
 may be extension issueMoin Malek– Moin Malek2017年10月26日 13:14:32 +00:00Commented Oct 26, 2017 at 13:14
- 
 Thank you, but we have checked that alreadyuser38833– user388332017年10月26日 13:39:48 +00:00Commented Oct 26, 2017 at 13:39
- 
 Please cross check that block class name have backslashes if there Magento does not support backslashMoin Malek– Moin Malek2017年10月26日 13:44:08 +00:00Commented Oct 26, 2017 at 13:44
- 
 You mean this? <referenceContainer name="sidebar.main"> <block class="Blue\Theme\Block\Category\Leftcategory" name="left.menu" template="Blue_Theme::callouts/leftmenu.phtml" before="-" ifconfig="blue_settings/leftcolumn/isenable" /> </referenceContainer>user38833– user388332017年10月26日 14:21:53 +00:00Commented Oct 26, 2017 at 14:21
- 
 Did you resolve this?sudopratt– sudopratt2018年01月31日 00:23:43 +00:00Commented Jan 31, 2018 at 0:23
2 Answers 2
If there is any tag inside tag then will though mentioned error
just remove block then it works fine
you may search in your layout files reference for <head>.
Once you have found some layout files that has the <head> reference. 
In these files, you may check that there is no block definition within the head node. If there is a block, either comment it or remove it (you may backup your layout file of course)
The reasoning is that head has indeed title subnode, css and so on.