The way IPS loads it's classes is by prefixing their original classes with a unique character (an underscore), then loading all the plugins/hooks and patching them over the original class, then patching an empty class with the proper name at the end. For example, IPS\_Output would be extended by IPS\hook123 which would then be extended to IPS\Output (which would be blank), so that all the hooks (in the order they are installed I believe), are loaded before creating the right name for the output. By the looks of this error message, one of your hooks/plugins got deleted or uninstalled improperly, and now it can't find it while it's trying to patch it.
I've never experienced this issue before, but your best bet would be to check that all the plugins you have installed are installed correctly, and if you deleted any plugins, make sure they are actually out of your script so that IPS has no way of knowing that it ever existed in the first place. Look inside your /plugins/hooks.php file and look for the numeric ID 489 and see what it's looking for and what it's trying to override. Either delete that section of code in the file carefully to not mess up the rest of the file and then try again.