1. What other plugins are you running. There are for some reason other plugins that are also creating menus called 'Media-Tags' under the Library section.
I deactivated all plugins to single the issue out to this plugin. The plugins are:
- Akismet 2.5.3
- Enable Media Replace 2.5
- Lock Pages 0.2.2
- Media Tags 3.0.5
- SexyBookmarks (by Shareaholic) 184.108.40.206
- Widget Context 0.7
- WordPress jQuery UI Effects 1.0.0
2. What hosting are you using? Windows? WordPress standard or WordPress Multisite?
Windows hosting (it's a development server, real hosting is on Linux CentOS). WordPress standard.
3. What theme?
Custom, but I switched it to twenty eleven 1.2 to verify that it isn't the theme causing the issue. At the moment I have everything disabled except your plugin.
4. Are you accessing the wp-admin will full admin access? Since version 3.0 of Media-Tags it support roles-based access. By default only full admin users have access to the Media-Tags menu panel. But full admin user can grant access to non-admin users via the Media-Tags menu.
Full admin access.
Your plugin works on a fresh installation of WordPress (on the same server).
I have just reinstalled the latest WordPress update (via updates tab) and deleted your plugin files and re-downloaded to ensure that they are fresh. Switched to twenty eleven theme and removed all plugins (except yours) and it still doesn't work.
No menu item, and no integration into the media editor. Media tags still shown on manager interface though. So your plugin is partly working.
It is strange because the plugin was working before I updated WordPress and your plugin.
Please let me know if there is any other information that you need.