Saving Menu causes 500 Error

What does it say in the error_log?

[Sat Jul 11 10:41:18 2015] [###] [fcgid:warn] [client ###.###.###.###:#####] mod_fcgid: read data timeout in 120 seconds, referer https://mywebsite.org/wp-admin/nav-menus.php
[Sat Jul 11 10:41:18 2015] [###] [core:error] [client ###.###.###.###:#####] End of script output before headers: nav-menus.php, referer https://mywebsite.org/wp-admin/nav-menus.php

IT is possibly a memory issue, try upping the memory allocation

First, increase the memory available to WordPress:

https://codex.www.ads-software.com/Editing_wp-config.php#Increasing_memory_allocated_to_PHP

If this fails, try increasing the memory available to PHP:

https://tutorials.hostucan.net/how-to-increase-php-memory-limit/

You might also need to look at post_max_size

https://mediatemple.net/community/products/dv/204404784/how-do-i-increase-the-php-upload-limits

IT is possibly a memory issue, try upping the memory allocation

First, increase the memory available to WordPress:

https://codex.www.ads-software.com/Editing_wp-config.php#Increasing_memory_allocated_to_PHP

If this fails, try increasing the memory available to PHP:

https://tutorials.hostucan.net/how-to-increase-php-memory-limit/

You might also need to look at post_max_size

https://mediatemple.net/community/products/dv/204404784/how-do-i-increase-the-php-upload-limits

IT is possibly a memory issue, try upping the memory allocation

First, increase the memory available to WordPress: https://codex.www.ads-software.com/Editing_wp-config.php#Increasing_memory_allocated_to_PHP

If this fails, try increasing the memory available to PHP: https://tutorials.hostucan.net/how-to-increase-php-memory-limit/

You might also need to look at post_max_size: https://mediatemple.net/community/products/dv/204404784/how-do-i-increase-the-php-upload-limits

IT is possibly a memory issue, try upping the memory allocation

First, increase the memory available to WordPress: https://codex.www.ads-software.com/Editing_wp-config.php#Increasing_memory_allocated_to_PHP

If this fails, try increasing the memory available to PHP: https://tutorials.hostucan.net/how-to-increase-php-memory-limit/

You might also need to look at post_max_size: https://mediatemple.net/community/products/dv/204404784/how-do-i-increase-the-php-upload-limits