OSX 10.8 (Mountain Lion) and newer includes a feature called
Gatekeeper. This is a useful security feature. By default, Gatekeeper requires App developers to either:
* Obtain a Developer ID from Apple and use it to sign their applications.
* Distribute the software through the Mac App Store
Or else the applications will not launch when you just click on them in the Finder (or the Dock or whatever). You get this dialog when you try:
This is useful because it prevents malware from being able to run easily and automatically. Because developers must obtain an ID from Apple, if a developer "does bad things", Apple can revoke their ID and disable their bad acting applications. I encourage everyone to keep this feature enabled, because it is easy to work around if you need to run an application from an "unknown" developer.
Media Center is signed, but JRiver does not currently have a working Developer ID from Apple. So, if you have Gatekeeper enabled, it will show this error the first time you try to launch the application. This does not mean JRiver is "bad" in Apple's eyes, it just means that they don't have a registered Developer ID for JRiver.
Working around this is simple. The first time you launch any particular version of MC, you must locate the application itself in the Finder. Right-click (or hold the Control key and click if you have a terrible mouse) and choose
Open. This "overrides" the normal Gatekeeper behavior, and allows you to run any application you want. OSX will present the same warning shown above, but this time, there will be an Open button you can click. You only need to do this once per version of MC, and this "override" will be remembered from then on out.
Further information:
http://www.imore.com/how-open-apps-unidentified-developer-os-x-mountain-lion