Simon,
I'll be moving this to the JLinked / Joomla 2.5 support area after I post this. I'm assuming you are working with those versions and just accidentally posted in the JFBConnect forums. If you are using JFBConnect, let us know.
As for your issue, can you let us know when you get that error? Is it when you install the extension, configure something, or simply click the Login with LinkedIn button? Is there a page we can look at?
Finally, that message is obviously very vague. Here are some things you can do to help narrow down the actual cause:
* Disable any JLinked Profile plugins you aren't using. Specifically, if you have the JLinked Profiles - Community Builder plugin enabled, but don't have Community Builder, disable that plugin. Do that for all profile plugins you shouldn't need enabled.
* If that doesn't work, go into the Joomla Global Config area. Turn off GZip compression and set Error Reporting to 'Maximum'. Recreate the problem and see if a better, more descript, error message appears. If so, let us know what it is.
Hope that helps!
Alex