http://po.clancentral.us/viewtopic.php?p=55292#p55292

Change some settings on your NIC card will normally resolve the issue. Yes, it is most likely server side, however it can be managed client side.

As said, I have solved the issue with random R0 and Error 30002. It was some settings on the actual network interface card for the computer I have running FFXIV.

These are the settings, and what they are set to for stopping Error 30002.

Flow Control = Disabled
Interrupt Moderation = Disabled
Priority & VLAN = Disabled
To get to these settings, they are usually located in the Advanced tab of your Networking Controller in Device Manager.

1. Right Click My Computer or just Computer
2. Select Manage
3. Click on Device Manager
4. Expand the Network adapters list
5. Double Click on the network adapter listed (if you have more than one and not sure which one, just do this to all of them EXCEPT for wireless network cards)
6. Click on the Advanced tab
7. Select Flow Control and set the Value to Disabled
8. Select Interrupt Moderation and set the Value to Disabled
9. Select Priority & VLAN and set the Value to Disabled
10. Click OK
11. Reboot!