I have been facing problem in all my wordpress installations. I am unable to view some plugins in the plugin admin panel of the wordpress installation. I did do some googling but could not find a solution. Just now I was upgrading some of my plugins and deleting all the plugins which I was not using. Once I deleted a few plugins, I could get the missing plugins in my admin panel and could activate it. I am having the same problem with my theme editor. The theme editor is broken for some themes. I need to use an external editor to edit my themes.
I had the same problem with my drupal installation. Its confirmed that the problem is with the server. I have got a solution for Drupal for missing modules
Do anybody have solution for Missing plugins in Wordpress? If you can help me in this it would be great. If I come up with a solution for this, surely I will post it here.

