Customizer shows Internal Server Error

Hello, when I am using Customizer to customize my Kathmandu, I am not seeing the window which shows my site as I customize. Instead I get a blank window and it says: Internal Server Error The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator, and inform them of the time the error occurred, and anything you might have done that may have caused the error. More information about this error may be available in the server error log. Here is an image of the screen: https://storage.googleapis.com/leslie_storage/Internal%20Server%20Error.jpg I was using the Customizer just fine when the error occurred. I tried Deactivating plugins. Here are the plugins I am using: Akismet Catch Updater Jetpack PHP Compatibility Checker Responsive Accordion & Collapse Simple 301 Redirects Updraft WP-Optimize Yoast seo