Blank edit page with 4.1.1

Blank edit page shows following message instead of editor: Fatal error: Out of memory (allocated 28311552) (tried to allocate 14 bytes) in /homepages/25/d210714655/htdocs/2012/wp-includes/post.php on line 2087

Have done:
Reinstallations of 4.1.1
Deactivated all plugins, deleted old ones, Activated new ones, then deactivated them all
Updated PHP server to 5.5
Already on custom theme

These attempts seem to have improved things slightly, since used to be just blank.
Now the above error message appears.
Here is the live url of the concerned page: https://www.laclinique.net Live version is displaying as last saved version fine. But now I need to do some changes, like everyday!

Please Help!!!