Hi mswtmgr1,
Thanks for reaching out!
This can be caused by many things using your memory. So lots of plugins, busy site, resource intensive code in plugin or themes, etc.
Likely it gives you an error message with The Events Calendar because the memory gets full by the time it gets there.
You also mentioned that when you change to a different theme than Divi, then the problem is solved. What you can also try is leave Divi on and deactivate other plugins than TEC. Does the error also disappear.
I’ve seen similar cases before and usually it wasn’t a specific plugin that caused the issue, but rather the memory needed by all the plugins and theme was not enough, so after activating the n-th plugin (no matter which one) the server said “Sorry, I can’t handle that.”
If this is the case then you can try to increase the memory limit in php. Also it might be helpful to add the following two lines into your wp-config.php file:
define( 'WP_MAX_MEMORY_LIMIT' , '512M' );
define( 'WP_MEMORY_LIMIT' , '512M' );
Let me know what you find.
Cheers,
Andras