Just wanted to follow up on this. Please see our posts above for an overview of steps to take if you're having this issue. Even with those steps, it's still affecting some users, so we just wanted to pass along a quick and sure solution. This involves editing the plugin code, so we've tried to word this so even those without coding knowledge can figure it out:
1) Log in to your site
2) Go to Plugins > Editor
3) Select NextGEN Gallery from the drop down at upper right.
4) Make sure the ngggallery.php file is highlighted on the right hand list of files
5) Scroll down about 100 lines in the nggallery.php, just comment out the relevant line by doing this:
add_action('admin_init', array(&$this, 'display_update_notice'));
// add_action('admin_init', array(&$this, 'display_update_notice'));
That is, just add // in front of the line and save your file.
That will solve your issue. As always when editing files, we recommend that you back up your files. If not, at least ensure you have a copy of the NextGEN Plugin on your own computer. That way if you go in there and do something else that affects your site or functionality, you can easily return the ngggallery.php file to it's original.
The announcement will no longer be needed and will be removed in the next update.