Editor goes blank after entry, and preview gives 404 error

I upgraded to PHP v5.6 and no longer get a php error or warning. However, the symptoms remain when I enter a You Tube url in perch admin; namely that on clicking save the screen goes blank and the YouTube video is not embedded.

For older perch regions, I am now also getting a blank page after saving, but the entry (in a textblock) is successfully added to the page. For both an old textblock region and the new YouTube region, View Page gives me a 404 error. For the textblock, it's at https://www.newcitychiropractic.com/perch/core/apps/content/edit/www.newcitychiropractic.com/resources.php (which I suppose is the draft page address), rather than the actual page's URL.

Seems like a configuration error that I can't figure out, but also the YouTube embed fails, whereas the textblock succeeds. And View Page from admin fails in both cases.

Here are the entries in the php error log:

[06-Sep-2016 15:51:32 UTC] PHP Warning: simplexml_load_string(): Entity: line 1: parser error : Start tag expected, '<' not found in /home5/newcity4/public_html/perch/addons/fieldtypes/youtube/youtube.class.php on line 180 [06-Sep-2016 15:51:32 UTC] PHP Warning: simplexml_load_string(): No longer available in /home5/newcity4/public_html/perch/addons/fieldtypes/youtube/youtube.class.php on line 180 [06-Sep-2016 15:51:32 UTC] PHP Warning: simplexml_load_string(): ^ in /home5/newcity4/public_html/perch/addons/fieldtypes/youtube/youtube.class.php on line 180 [06-Sep-2016 15:51:32 UTC] PHP Fatal error: Call to a member function xpath() on boolean in /home5/newcity4/public_html/perch/addons/fieldtypes/youtube/youtube.class.php on line 182

youtube.class.php:

        if ($xml_string) {
            $xml = simplexml_load_string($xml_string);

            $c = $xml->xpath('*/media:content[@type="application/x-shockwave-flash"]');

Debug message on entry to admin: SELECT u.*, r.* FROM perch2_users u, perch2_user_roles r WHERE u.roleID=r.roleID AND u.userEnabled=1 AND u.userID=1 AND u.userHash='097a52f08154be502e8b329a5f5fd23d' LIMIT 1 UPDATE perch2_users SET userHash='b5e3e19f462866a397f0f9fdf938a41f' WHERE userID='1' [29] SELECT p.privKey FROM perch2_user_privileges p [18] SELECT * FROM (SELECT DISTINCT settingID, settingValue, userID FROM perch2_settings WHERE userID=1 OR userID=0 ORDER BY userID DESC) AS settings GROUP BY settingID, settingValue, userID [1] SELECT * FROM perch2_content_regions WHERE regionID=18 LIMIT 1 [1] SELECT * FROM perch2_pages WHERE pageID='11' LIMIT 1 [1] SELECT * FROM perch2_content_items WHERE regionID=18 AND itemRev=7 ORDER BY itemOrder ASC [1] SELECT * FROM perch2_content_items WHERE regionID=18 AND itemRev=7 ORDER BY itemOrder ASC Using template: /templates/content/video.html Form not posted or did not validate Setting alert: You are editing a draft. Preview (draft)

So I take it that Perch is not happy with the template. The template is as follows:

<perch:content id="addvideo" type="youtube" width="420" label="YouTube URL" output="embed" />

After entry of the YouTube URL and save, the page goes blank so there are no debug messages.

Doesn't seem to matter which URL: https://www.youtube.com/watch?v=y60wDzZt8yg

I am working on a webhosting server -- I copied an html page, put a php extension on it, included perch/runtime and added a perch region to it. Once it's working, I'll replace the html page with the php page in the navigation.