Custom party plugin might cause problems, do you use any ?
When the page is viewed, firebug raises :
uncaught exception: Error: Permission denied <https://apps.facebook.com> to get the property Proxy.InstallTrigger
cr is not defined
[Stop on error] cr.createRuntime("c2canvas");
The second part (cr) means that the application can't be executed.
And that's because of the first part and the "Proxy.InstallTrigger" property.
Once again, it could come from a custom plugin/behavior. If you use some, please list them and get in touch with their author through the plugins' topic.
If it's a genuine C2 bug Ashley should have a look at this.