An AJAX request terminated abnormally.

I've "drush'ed up" to 7.34. Everything is working well but for this problem. My system configuration check shows no errors. My site is running as a virtual server under apache and with SSL. A certificate is installed on my server and the certificate authority site checker reports that the certificate and web server are properly configured.

I've tried a number of things:
- increasing PHP timeout in php.ini
- increasing other counts mentioned online in php.ini
- fiddling with all manner of combinations of rewrites and base_urls.
- check apache logs -- nothing
- check drupal logs -- nothing

The problem occurs consistently on admin > structure > panels edit.... When I click on "summary" for example, to view the summary for a page template, I get a spinning dial and then the error. I also get this error on admin > structure > pages, when I enter a search term for pages of interest.

As for what seems the most common explanation -- a mismatch between url rewrites by .htaccess and the setting of base_url in settings.php, here are the details for my site. They look right to me, but maybe I'm just being a dolt. Note that I am forcing https. Any help, either fixing or even just debugging this problem would be a big help.

My settings.php file sets base_url as follows:

$base_url = 'https://www..com'; // NO trailing slash! ( is replaced by my web site name)

The relevant parts of my .htaccess looks like this:

RewriteEngine on

# Rewrite http to https uniformly
RewriteCond %{HTTPS} off [OR]
RewriteCond %{HTTP_HOST} ^kevinjsullivan\.com*
RewriteRule ^(.*)$ https://www.kevinjsullivan.com/$1 [L,R=301]

# Set "protossl" to "s" if we were accessed via https://. This is used later
# if you enable "www." stripping or enforcement, in order to ensure that
# you don't bounce between http and https.
RewriteRule ^ - [E=protossl]
RewriteCond %{HTTPS} on
RewriteRule ^ - [E=protossl:s]

# Make sure Authorization HTTP header is available to PHP
# even when running as CGI or FastCGI.
RewriteRule ^ - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]

# Block access to "hidden" directories whose names begin with a period. This
# includes directories used by version control systems such as Subversion or
# Git to store control files. Files whose names begin with a period, as well
# as the control files used by CVS, are protected by the FilesMatch directive
# above.
#
# NOTE: This only works when mod_rewrite is loaded. Without mod_rewrite, it is
# not possible to block access to entire directories from .htaccess, because
# is not allowed here.
#
# If you do not have mod_rewrite installed, you should remove these
# directories from your webroot or otherwise protect them from being
# downloaded.
RewriteRule "(^|/)\." - [F]

# If your site can be accessed both with and without the 'www.' prefix, you
# can use one of the following settings to redirect users to your preferred
# URL, either WITH or WITHOUT the 'www.' prefix. Choose ONLY one option:
#
# To redirect all users to access the site WITH the 'www.' prefix,
# (http://example.com/... will be redirected to http://www.example.com/...)
# uncomment the following:
# RewriteCond %{HTTP_HOST} .
# RewriteCond %{HTTP_HOST} !^www\. [NC]
# RewriteRule ^ http%{ENV:protossl}://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
#
# To redirect all users to access the site WITHOUT the 'www.' prefix,
# (http://www.example.com/... will be redirected to http://example.com/...)
# uncomment the following:
# RewriteCond %{HTTP_HOST} ^www\.(.+)$ [NC]
# RewriteRule ^ http%{ENV:protossl}://%1%{REQUEST_URI} [L,R=301]

# Modify the RewriteBase if you are using Drupal in a subdirectory or in a
# VirtualDocumentRoot and the rewrite rules are not working properly.
# For example if your site is at http://example.com/drupal uncomment and
# modify the following line:
# RewriteBase /drupal
#
# If your site is running in a VirtualDocumentRoot at http://example.com/,
# uncomment the following line:
# RewriteBase /

# Pass all requests not referring directly to files in the filesystem to
# index.php. Clean URLs are handled in drupal_environment_initialize().
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !=/favicon.ico
RewriteRule ^ index.php [L]

# Rules to correctly serve gzip compressed CSS and JS files.
# Requires both mod_rewrite and mod_headers to be enabled.

# Serve gzip compressed CSS files if they exist and the client accepts gzip.
RewriteCond %{HTTP:Accept-encoding} gzip
RewriteCond %{REQUEST_FILENAME}\.gz -s
RewriteRule ^(.*)\.css $1\.css\.gz [QSA]

# Serve gzip compressed JS files if they exist and the client accepts gzip.
RewriteCond %{HTTP:Accept-encoding} gzip
RewriteCond %{REQUEST_FILENAME}\.gz -s
RewriteRule ^(.*)\.js $1\.js\.gz [QSA]

# Serve correct content types, and prevent mod_deflate double gzip.
RewriteRule \.css\.gz$ - [T=text/css,E=no-gzip:1]
RewriteRule \.js\.gz$ - [T=text/javascript,E=no-gzip:1]

# Serve correct encoding type.
Header set Content-Encoding gzip
# Force proxies to cache gzipped & non-gzipped css/js files separately.
Header append Vary Accept-Encoding