You're running a broken/incorrectly-packaged add-on, or the add-on(s) in question is/are calling a file that doesn't exist (or has been unloaded from the .exe file, which you can see just under the IRC window you have open).
Alternatively you are trying to load an add-on from someone else's server that contains a file that the file manifest cannot download. I've had this problem with Heedicalking's Hind vehicle.
