I mean serverside code caching like APC or Zend OpCache (native PHP 5.5 caching)

Here are a few more things to check:

Looking at the screenshot, with the admin screen squashed as it is, I've seen similar "Layout problems" when error messages are spat out to the browser, before the CMS' AJAX / PJAX responses are passed to the browser. So using your browsers' developer tools, do you see any errors in the markup of the CMS but that obviously aren't visible (due to styling the text the same colour as the background for example)? If there are, post these and/or try and debug what's happening yourself.

The CMS basically sends and receives large junks of JSON that _may_ be being truncated for some reason. These JSON chunks tell the CMS what screen to show, what state it's in etc etc. If they are corrupted or changed part way through a request for some reason, weird layout issues can result. Again, using your browsers' developer tools, examine these JSON hunks, and ensure they're not truncated or invalid. You can check for validity by copy/pasting the JSON into something like JSON Lint Pro (http://pro.jsonlint.com/).

Let us know how you get on.

Hi Guys,

Thanks for the input therussdotcom, but we couldn't see any errors in the development tools.

I've got this working anyway, but didn't really get to the underlying problem unfortunately.

In the end, here is what I did to get the website working:

1. Created a new account on our alternative server, this time using the correct url for the primary domain.
2. Copied the database over to the new account (exported from old db to new db using phpMyAdmin).
3. Uploaded the latest version of SilverStripe (it was 3.1.6 but we upgraded to 3.1.9).
4. Uploaded all the theme/website files.
5. Modified the mysite/_config.php to the correct database settings.
6. Parked a temporary domain on the account to check the site was working.
7. Did a dev build on the website.
8. Changed the primary domains DNS to point to the new server.
9. Login in to the admin panel using the primary domain and all is good.

I do realise several things have changed, like the silverstripe verison, the server, etc. But in order to get this working for the client, I had to try what ever would work.

We do have another site with the same issue and if we managed to sort the problem there I'll post an update.

Thanks for all the help guys!