We recently opened up an account with WPMUDEV and uploaded the one of the theme packs along with a few plugins. Until we did this, the site was running fine. However, since then the entire install appears to be broken and we can't seem to get it fixed.
Basically, what is happening is we install a handfull of the themes and a few hours later the "presentation" tab and "plugin" tab becomes broken. When you click on it from any user account it simply tries to download a file or displays a blank page.
Yesterday we stripped out all of the plugins and themes and it started working properly. However, once we started uploading themes again the same thing happened.
Not only is it causing problems with the presentation and plugin tabs in the admin control panel, but it's also causing some of the blogs to crash.