[Steven Zahm]

@ John

Have set a directory home page?

Are all the Connections addons, extensions and templates up to date?

Can you please try:

• How do I check for a theme conflict?
• How do I check for a plugin conflict?

Also, it is possible the memory allocated to PHP is being exhausted. The Customizer does require more resources.

Here’s is a blog post which covers several ways to increase the memory. Which method will work depends on the web host. My suggestion is to start at the top of the list an work your way down.

http://dailyblogging.org/wordpress/increase-wordpress-memory-limit/

Please let me know the results.