Everyone knows it is networking issues. I am sharing my experience so that it may help others narrow down the problem.

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I have three PC boxes with 3 separate accounts so that helps when there are issues. Two are Win 10 and one in Win 7. They all go through the same switch connected to a router which is connected to a cable modem. The other day one of the Win 10 started disconnecting, 90002. I could not stay connected for more than a few minutes. I tried it the next day and it worked fine so I thought it was just a hiccup. All the time the other two accounts had no problems so I knew it was something with the PC that account was on. I changed my virus software thinking it might have something to do with it because I was getting a message that it could not set the firewall and after trying a few things gave up on it and installed a new virus program. The firewall issue was gone but I was still getting the 90002 after logging in and now I was getting 2002 where I could not log in my character. I re-checked everything and made sure ffxiv was being allowed through the fire wall. It had all been set up automatically and it all looked OK.

[What seems to have fixed it for me]
I decided to dive into the networking and discovered that wireless was enabled. I didn't need wireless because I had an ethernet connection so I went into device manager and 'disabled' it. I logged into my account it is still working some 20 minutes later with no issues. (Before posting this I logged out and back in and everything is working fine.)

[More Blah Blah Blah]
Before you get too excited, I checked the other two PCs and found the Win 7 did not have wireless enabled but the other Win 10 did. It had even found more wireless connections than the problem Win 10 and I have not had any issues with the other Win 10 machine, so I can say my solution is definitely not a cure all. I will be disabling the wifi on the other Win 10 machine because it is not needed and will free up any resources it is using. I cannot say why disabling the wifi on the problem win 10 fixed my 2002, 90002 issues. I am thinking it may have caused the PC to not respond to the SE server and cause it to drop me. There is probably some setting somewhere that would allow them to coexist but I have no clue where that would be and don't have a need for wifi on the PCs anyway.

Welcome to the 21st century where the technology is amazing, when it works, and exceedingly frustrating when it does not. Like anything powerful, it is a two edged sword. Listen to some Hang Massive if you can find it on YouTube and need a break.

I like it when I am the problem, I'm easy to fix. :P