Tom Tom

Problem solved. Within the function.php a function fb_restrict_mime_types disturbed the whole process.

The network’s activated plugins are:
Advanced Custom Fields
Edit Author Slug
HTML5 Boilerplate
PS Disable Auto Formatting
SwfObj
Widget Logic
WordPress Importer
WP Show IDs

There are two “old” blogs BOTH which don’t resize the images, one “new” blog, invented AFTER the update, which is working without problems. The same image is resized in the “new” blog, but not in the “old” ones.

btw, these plugins are NOT activated in the blog mentioned above

Advanced Custom Fields
Edit Author Slug
HTML5 Boilerplate
PS Disable Auto Formatting
SwfObj
Widget Logic
WordPress Importer
WP Show IDs

No, i get this error four or fife times. And yes, just the full one.

In the error.log is just this:

[31-Jan-2013 08:06:30] PHP Notice: has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0! Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /homepages/14/d337169883/htdocs/_www2012/wp-includes/functions.php on line 2923

All files within /blogs.dir/ are set to 660, all directories to 777.

Well, none. So either installing or?

I read, that ImageMagick is preferred by WordPress 3.5, that might be a nice feature (or not, don’t know), but it would be as nice to throw out some warning if a required function like ImageMagick is not installed.

GD is installed: bundled (2.0.34 compatible)

And yes, you’re right, the hoster is not a classy one.

Should have been 3.4, now it’s 3.5, the server is 1&1 Business Package:

Linux infong 2.4 #1 SMP Fri May 18 17:32:59 UTC 2012 i686 GNU/Linux Build Date Aug 14 2012 10:30:28

No resizing plugins, just plain Media.