AJAX Error On Next Month Button

We have events set out in to the future on our calendar. When you click the “Next Month” button, the following error appears.

Missing arguments in default calendar grid ajax request.

I have already run through the standard troubleshooting steps, including disabling all other plugins and switching to TwentySixteen.

http://www.stjohnslaverne.org/this-week-at-saint-johns/

### WordPress Installation ###

Site Name: Saint John's Episcopal Church in La Verne
Home URL: http://www.stjohnslaverne.org
Site URL: http://www.stjohnslaverne.org
Version: 4.6.1
Locale: en_US
Timezone: America/Los_Angeles
Multisite: No
Permalinks: /%postname%/
WP Memory Limit: 40 MB
WP Debug Mode: No
Script Debug: No

### Active Theme ###

Theme: saint_johns - 1.0
Child Theme: No
Parent Theme: -

### Active Plugins ###

Yoast SEO: 3.8
All In One WP Security: 4.1.9
NextGEN Gallery: 2.1.56
Widget Context: 1.0.4
Simple Calendar: 3.1.8
Employee Scheduler: 1.9.4
Akismet: 3.2
Special Recent Posts FREE Edition: 2.0.4
TinyMCE Advanced: 4.4.1
WordPress Importer: 0.6.3
WP-ServerInfo: 1.63
Jetpack by WordPress.com: 4.3.2
Contact Form 7: 4.5.1

### Server Environment ###

Web Server: Apache
PHP Version: 5.3.28
MySQL Version: 5.5.53-log
Server Timezone: UTC
Display Errors: No
Memory Limit: 256M
Upload Max Filesize: 250000000
Post Max Size: 250000000
Max Execution Time: 30
Max Input Vars: 1000
fsockopen: Yes
cURL: 7.36.0
OpenSSL/1.0.1e
SOAP: Yes
SUHOSIN: No
WP Remote POST: Yes
WP Remote GET: Yes

### Client Information ###

IP Address: 64.29.145.73
Browser: Firefox 49.0 (Windows)