HTTP Error with media uploader

Out of the blue I have a problem uploading images to a wordpress installation and I am getting the dreaded “HTTP Error” when using any of the built in uploaders I have tried everything on this support page.

I have also:

1) deleted my wp-admin and wp-includes folders
2) downloaded a fresh copy of WP 3.8.1
3) uploaded the deleted directories fresh
4) changed permissions on my wp-content/uploads folder to 755, and then to 777 just to see if it helps
5) created an .htaccess file with the mod-security fix language in it and uploaded it to my domain root, the WP root, and the wp-admin directory.
6) set the permissions for the .htaccess files above to both 755 and 777
7) recreated the same problem in different browsers and on different computers.
8) tried uploading smaller images
9) deleted my “uploads” folder, removed all entries from the Media Library, and tried a brand new upload.

Here’s the thing. In a final effort to fix this issue I made created a new virtual host on the server, installed a fresh copy of wordpress, imported the posts and pages from the main site, and re-uploaded all the images. So now I have two copies of the same site – one under https://www.mydomain.com and the other under new.mydomain.com, both on the same server, but under different vhosts.

The media uploader on new.mydomain.com worked just fine, so I swapped the two sites over and pointed the new site to https://www.mydomain.com

The media uploader stopped working. However, the old site (now under new.mydomain.com) started working…

Whichever way I set them, the https://www… stops working and https://new… works just fine

I’m sure there is a really obvious issue that I can’t see as a result of spending too much time going round in circles. Can anyone point me in the right direction please!

Thanks

The working site is https://new.julieanneimages.com