Hi,
Here is a patch until the team of the Jetpack plugin fix this issue.
Edit the file /wp-content/plugins/jetpack/modules/custom-css/custom-css.php, and change the line 388
if ( ! is_super_admin() && ( 1 == $current_blog->spam || 1 == $current_blog->deleted ) )
to this
if ( ! is_super_admin() && isset($current_blog) && ( 1 == $current_blog->spam || 1 == $current_blog->deleted ) )
It works in my WordPress 3.4.1 installation.
