Running Windows 8.1 on Intel i7 quad core with 12GB RAM. CC updated to 2015 Premiere Pro and Creative Cloud App is installed. Everything is up to date. Fresh install of Adobe Extension Manager ver 184.108.40.206. Rebooted. Opened Premiere Pro. Closed Premiere Pro. Downloaded the Pond5 extension twice.
Still will not load using Extension Manager. All I get is a bit of whirring and then, each time, this error: Failed to install the extension 'Pond5PPRO'. Please make sure the manifest.xml of this extnesion is valid and the Extension Manager recognizes at least one product which the extension supports."
This resolved itself ... it turns out that the Extension Manager, which has no visible "update" function, needed updating. The Creative Cloud App did update it. However, it took three reboots and one full day before the App recognized Extension Manager and updated it.
if you have problems with installing this and other plugins, it could be because Extension Manager is no longer supported and may not work anymore for CC2015.
There's an open source installer which seems to work which van be found here: Site - Zxp Installer