Cheatin Uh error

I’m getting the Cheatin’uh error message when I try to preview or customise themes in any way, which is really rather annoying!

I have done (or rather my techie husband has!) the following, based on a list we saw posted when we googled the error message:

– deactivating ALL plugins temporarily to see if this resolves the problem – made no difference

– If that does not resolve the issue, try switching to the unedited default Twenty Fourteen Theme – made no difference, still does it regardless of which theme.

– If that does not resolve the issue, try resetting the plugins foldervia FTP or SFTP or whatever file management application your host provides. Sometimes, an apparently inactive plugin can still cause problems (because the hooks remain unless plugins completely removed or some plugins stick around in cached files. So by renaming the folder, you break them and force them inactive). – again, made no difference at all.

– If all the above steps do not resolve the issue, then try MANUALLY re-uploading all files and folders EXCEPT the wp-config.php file and the /wp-content/ directory from a fresh download of WordPress. Make sure that you delete the old copies of files & folder before uploading the new ones. Read the Manual Update directions first!

– running the upgrade manually via wp-admin/upgrade.php

So, um, help! What do I try next? I’ve tried multiple themes, including the WP standard ones. I’m running 4.4, if that changes anything?

I’ve tried deleting all the plugins, and then trying the twenty sixteen theme, and I get the same thing…