I also have this issue, but I’m not running Multisite. I’m running NextGen Version 2.0.31 and I have a local and production version of the identical website running. The local version (I’m using my hosts file to do local development) does not work and shows https://d.pr/i/ZalS and the production version does work, showing https://d.pr/i/cDP4
I am using the same Google Chrome Version 30.0.1599.69 and Safari Version 6.0.5 to view each site on Mac OS X Mountain Lion. Both browsers display the same issue, so this clearly is not a “You browser doesn’t have Flash, Silverlight, HTML5, or HTML4 support.” issue as the error insists.
EDIT: I can also confirm this problem exists in Windows running IE8 or IE10 when running a site locally (No multisite still though).
I did submit a bug ticket, but was not given a ticket number to reference.