Editing anything gives 500 error: can't GET /index.php/ccm/system/block/render ....

I've put up a new v8 site; it's super simple, 2 pages, cloneamental theme, two add-ons (block designer and background image) and a few modifications. (I'm new to v8, but have done other concrete 5 sites, with earlier versions).

When I load the page and start editing, everything is fine. However, when I save an edit, I get a 500 failed to load resource error:
GET http://www.example.com/index.php/ccm/system/block/render?cID=198&arEnableGridContainer=0&bID=354&arHandle=Main+%3A+56 500 (Internal Server Error)

and I'm unable to edit further, unless I refresh the page. It's possible to edit content and use the site, but I have to refresh the page after every edit, which isn't ideal.

I've searched the source code of my theme and add-ons, and can't find the problem... I'm totally stumped.

Any help or advice will be greatly appreciated!

Extra environment details;
v 8.1.0
php v 5.6.32

View Replies:
MrKDilkington replied on at Permalink Reply
Hi talia7,

To get more information about the error, temporarily enable debug errors.
Dashboard > System & Settings > Environment > Debug Settings > Error Detail > Show the debug error output

If you are using Chrome, you can right click on the error in the browser console, then select "Open in new tab" from the right click menu. This will display an error screen and should tell you where the error is.
talia7 replied on at Permalink Reply
Thanks MrKDilkington.

Unfortunately, the toolbars remain disabled after editing anything, so I can't access any debug error information.

I think I'm starting to understand the error a bit better, though I'm no closer to resolving it.

For reasons I don't understand, I'm getting a warning
Deprecation. Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience.

then the error, more detail below:
(anonymous) @ VM244:1
send @ jquery.js:5
ajax @ jquery.js:5
m.(anonymous function) @ jquery.js:5
c.refreshBlock @ app.js:3
c.success @ app.js:3
success @ app.js:3
c.success @ app.js:2
i @ app.js:2

It looks like the error is being caused by the deprecation of app.js?

Even if this is right, I've no idea what to do about it. Help appreciated!
MrKDilkington replied on at Permalink Reply

Did you follow the above steps to enable debug errors and right click on the "GET" error?

What modifications did you make and where did you make them?