No I have a dedicated server with Slicehost (which I believe is a Rackspace company). But I do have complete control of the server...
Does your doc root start with /mnt/ ?
no no, I have a dedicated server.
The site is in /var/www/vhosts/blah.com/public
my problem is fixed. It was the .htaccess Basic Authentification that broke the upload. After removing it everything works.
Which? Where is .htaccess?
In the document root I had a .htaccess file that I created to prevent access before the system is live. It seems as Uploadify cannot handle the authentification through AuthType Basic http://httpd.apache.org/docs/2.0/howto/auth.html or doesn't have recognition of it. So the upload fails.
If this is active on your server you will get a login screen from the browser before you see the website.
I was previously using ImageDataObjectManager and all worked fine. ! changed it to FileDataObjectManager and i now get the http error. If i change it back, it works again
I Found my problem. I had a class MyImage extending data object.
Now in Homepage.php i was adding a MyImage using a ImageDataObjectManager and in Page.php i was adding MyImage using FileDataObjectManager. When i changde them both to FileDataObjectManager or both to ImageDataObjectManager, it worked