I just had the exact same thing...

We are currently investigating application signing problems on Mac OS X that cause Mac OS X's Gatekeeper to flag Capture as broken. Until we have resolved this, the workaround is to go to the System Preferences and find the Security & Privacy settings. In there, please make sure that your "Allow apps downloaded from" setting is set to "Anywhere". After starting Capture once, remember to change the setting back to its original value.