If you've installed the debugging addons and get an error the BugSack icon will turn from green to red (that and you should hear a warning sound...get used to that
).
Clicking the BugSack icon will open the error frame with the last? error text displayed. You can select/copy/paste the error text here along with your code and maybe we can help you figure out why you got the error.
If you have several errors BugSack has Previous/Next buttons for moving through them and a button to limit the view to just the current errors.