The devs are looking into this issue please go to this thread:

Constant Disconnects for Many People can we please get some info?

... and provide the following information:

1) User Environment
1. – Operating System? (IE: WinXP, Vista, Win7, 32bit? 64bit?)
2. - Antivirus program? (IE: Windows Defender, AVG, etc)
3. – Internet Service Provider?
2) Exact Error Message
3) Frequency of 30002 Error?
4) What area were you in when the error occurred?
5) What were you doing when the error occurred? (What type of actions, movements, etc)
6) Were you in a party at the time the error occurred? (Please provide number of party members if you were in a party)
7) Estimate number of characters that were near you at time of error?
8) Were you able to log back into FFXIV after the error?

The information provided will be helpful for the Development Team to find a resolution to this issue.