I'm unsure as to what that error is and originally guessed it's because no one was playing. Each time i seek to play "For Fun" it gives me that error. However, as soon as i hit "For Glory" and "1vs1" i always get a match up right away. This is what led me to believe that people were simply not playing "For Fun" and had no match up built because of it
Many people play For Fun, I believe it gives the error more since it's harder to sync 4 people than two.(Also applies to FG smash).
Anyway, I believe the matchmaking issue's root of the problem can be from the kind of router too.
I've already tried 3 hotspots.
A ZTE PPPoE dial-up modem, paired with a CDR-KING router(yeah, crappy router, but works) : This one's connection is HEAVEN, but lackluster browsing experience. I barely get the error code at all. Unfortunately, my parents had to cut off the connection.
Huawei Mobile 3G Device : I get the errors. Though I suppose because the internet sucks more than the dial-up connection. But I get a variety of errors other than 516, like 514, 513, 502(this is different but just adding it in).
Huawei Echolife Bm622(The "modem" the ISP gave to us): error 0516, all the damn time. I used the methods I posted in the previous post. I'm starting to feel like Huawei devices have strict firewalls.
Also the ISPs here are different, but the ZTE and Echolife are sort of the same (Same company, but different sections, ZTE's landline, "modem"'s concerns mobile networks). The Mobile 3G device is from another ISP.
So... it might be on your router too, I heard that Belkin routers have odd firewalls. I guess I'll try to get another hotspot(not dial-up), maybe a 4G mobile device, to get this error fixed ONCE AND FOR ALL!