To take some pressure off the main thread, I'm starting this support topic to answer questions and hopefully fend off any repeat questions by answering them in the main post here.
Q: Nobody can connect and I get error code XXXXX!!
A: Make sure your ports are forwarded and that you can successfully ping them using an external tool. For information on how to forward your ports, see here. Certain numbers can mean different things. Check with Nintendo's website to see what the error code actually means as only a few actually pertain to ShinyGTS/ShinyDTS.
Q: What ports do I need to forward?
A: You need to forward Ports 80 [TCP] and 53 [uDP]. If you're unsure about the TCP/UDP indications, just forward both types on 80 and 53.
Q: I did forward my ports but nobody can connect still!
A: Make sure programs like Skype, Teamviewer and Apache Webserver [i have to include this for obvious reasons] are not running or have been configured to not use Port 80.
Q: I have no additional programs running, but people still can't connect!
A: Contact your ISP and see if they are blocking Port(s) 80 and 53. If they are, see if you can't ask them nicely to unblock the ports for your IP/account.
Q: I get an error from ShinyGTS/ShinyDTS while trying to start!
A: There are a few typical errors I've seen with ShinyGTS/ShinyDTS:
An error pertaining to an invalid path format. If you get this, change folders.
Permission denied. This means something else is probably using Port 80. Disable all programs that could possibly be using Port 80 and try again. Might also want to run as Administrator if error persists (Windows Vista & 7).
Q: Is Linux/Mac OSX supported?
A: Unofficially with Mono support. Mac OSX requires X11 to run any interface with Mono and I don't have a solid Mac system to test it on. I do not know if it actually runs on Linux or Mac OSX as nobody has really indicated to me that it does work. If someone wants to test it out and create a guide, that would be awesome. If you have issues with ShinyGTS/ShinyDTS on those platforms, I recommend IR-GTS.
[Thanks to evandixon!]
Q: I'm getting a .Net socket exception when trying to start the GTS server!!!
A: Make sure no other program is using port 80 or port 53. Developers: That means no IIS or Apache (unless you reconfigure them, see first Question for other programs).
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This list of questions can be modified or extended at any given time to answer any other frequently asked questions. Please do not hesitate to ask or post images pertaining to errors you might have.