When trying to open images from Bridge to camera raw the icon and the option in the drop down are both "dead" They open with a double click , so its just a niggle I could live without. Any clues?
That means there is something wrong with your install and you probably have no connection with Photoshop via a start up script. First check the menu Tools and see if Photoshop is in the list at the bottom. If not check Bridge Prefs to see if the start up script for Photoshop CS4 is there and you can add a checkmark to it.
Either way, the easiest go seems to restart Bridge holding down option key and choose reset preferences. This should bring the start up script for PS back in business.
In Bridge Prefs general you can check to set double click to open in ACR using Bridge. The drop down menu and the icon should be active also.
Be also sure you have only one version of ACR installed in the correct place. Open Photoshop and under the menu Photoshop check About plug in / Camera Raw. It should say ACR 5.xx (don't have CS4 anymore installed and not sure what the latest ACR for CS4 should be).
Should re loading the disc help?
Not if you don't deactivate, uninstall with removing preferences and use the Clean Tool:
to get rid of all presets and prefs for PS and Bridge. Reinstall does not always means resetting the preferences.
As Curt stated deactivate might not be necessary on the same machine but in this case you should do it by the book in the official way.
Can you report the exact versions you are using for Mac OS X and Adobe CS4 (PS, Bridge and ACR)