[abigailthefox]

We've had quite a few weird RoboRIO problems last season/this season, so I thought I'd just offer this quick checklist.

Step 0: Update your bridge firmware. If you are using the 2017 bridge that shipped with your KOP, your firmware needs to be updated if you have not already. Also, if you're using the 2016 bridge ( or anything older than that), you should update it as well.
Step 1: Reimage your RoboRIO. The WPI screen steps has an excellent set of instructions on how to do this.
Step 2: Reinstall the JRE on your robot (you stated you are a Java team). When you image the RoboRIO, the current JRE will be lost. Our team was getting some pretty ambiguous error messages, and it turns out we just forgot to reinstall the JRE after imaging.
Step 3: Try to connect to the RoboRIO in your browser. By typing in "roboRIO-####-FRC.local" (where #### is your team number with no leading zeroes, you should be able to get to the browser RoboRIO utility (this can also be used to ping the RoboRIO to test the connection. I recommend you try both).
Step 4: Use a different bridge. If you have access to a different model than the one you're using (i.e. if you've been using 2017, switch to 2016, and vice versa. You will also need to update the new bridge, if you haven't yet)
Step 5: Use a different RoboRIO (if you have one. These are expensive, and I know a lot of teams only have one. If this is the case, just skip this step. If you've tried absolutely everything and it's still not working, consider investing in a second RoboRIO. I would save this for when you're really desperate however, because it's not fun to be out $400 and then find that it didn't even solve your problem.)

Some other users have mentioned techniques for wrangling with the IP and firewall configurations. These are great steps to take, and I recommend taking them with someone who has experience with doing similar things, ideally a mentor or veteran student. Most of the things FIRST expects you to do (somewhat) routinely (such as imaging your RoboRIO or installing software) have great tutorials and documentation that help walk you through what you're doing. Messing with network configurations on a computer does not come with a nice made-for-FIRST guide, and it's easy to accidentally mess something important up. If you don't have a mentor who has IT experience, or a veteran student who knows about IP and network issues, then this is a great opportunity to tap your community for someone who can help you! Especially because once you make a partnership with a company/person who's willing to donate time and effort to help, you can go back to them as a resource in the future (because we all know that once one error gets resolved, it's only a matter of time before the next one rears it's ugly head).