just to clarify...is it tanking with a black screen, and saying "Downloading Data" or something like that in the corner?
And are you getting something along the lines of being unable to reach the lobby server or other connectivity related POL message?
I've seen this happen before for myself and others, and it was basically blocked internet traffic. Check logs to see if you can spot an IP being dropped--don't have the IP list on hand at the moment, but wanna say they were usually IP's starting with the number 124--can get ip info via someone like dnsstuff.com and get ARIN report showing who leased the IP--SE leases HUNDREDS of IP's in one big block. The fixes varied from correcting errors in port-forwarding rules, whitelisting the problematic IP (or a big block of SE's IP's), putting the system in the DMZ at the router(or physically bypassing the router and connecting directly to the modem) and using a software firewall on the system (whitelisting the SE IP's), or flat out replacing the router and setting up port-forwarding again.
If it is something that happens when it FIRST goes into 3D mode--as in after your last click in the POL interface to play, and it starts loading the title screen stuff, it could be simply a D3DInit error. POL often doesn't give you an error message for it and it just crashes to desktop and all you get is the Windows message about pol.exe stopped working. It happens a lot simply because the engine doesn't like the resolution settings--changing it to more standard resolutions usually fixes it.
If it's not a connectivity issue and is crashing after you've been in 3D mode for a bit, then it could be your video card, drivers, memory--any number of things hardware related and usually attributed to heat and/or voltage or just flat out failure of a particular component (bad cell in memory chip, etc.). Something like that can become a long list of things to check on--that's why I asked for a little clarification on just what you are seeing. Don't need to start testing every little thing if the router or local security is blocking UDP traffic from SE and there is an easy fix for that. Edit:
IP info for one of SE's blocks(just part of a LONG report):
Using 0 day old cached answer (or, you can get fresh results).
Hiding E-mail address (you can get results with the E-mail address).
% [whois.apnic.net node-3]
% Whois data copyright terms http://www.apnic.net/db/dbcopyright.html
inetnum: 22.214.171.124 - 126.96.36.199
descr: SQUARE ENIX CO., LTD.
descr: Shinjuku Bunka Quint Bldg.
descr: 3-22-7 Yoyogi, Shibuya-ku, Tokyo 151-8544,Japan
status: ALLOCATED PORTABLE
remarks: Email address for spam or abuse complaints *******@square-enix.com
changed: **********@apnic.net 20090818
So, you can try white-listing both TCP/UDP for IP's logged in the bolded range if a local firewall is blocking the traffic (or just do the whole block for that matter). NOTE: sometimes it isn't logged specifically as UDP or TCP traffic, it may simply be listed as a DNS or other ping activity--but for whatever reason, an expected response is lost and FFXI or SE drops the connection. Edit #2:
D3D crashes can also be tripped up by system/driver design issues--something causing a reset of the GPU. Something like ATI's PowerPlay kicking in and dropping the card back to 2D Mode clock speeds (lowers voltage to the GPU) after a set amount of time, and it can't sustain 3D support. One workaround for that is doing something to keep it in 3D Mode, like loading something else in the background or forcing clock settings in ATI TrayTools, locking it into 3D Mode clocks/voltages full time. Another culprit is the dual GPU setup like the Intel/nVidia mess we've started seeing on laptops in the last year or so. For that, you have to get new drivers that lock it to the nVidia GPU (not sure if they are still in Beta or not, but they are literally new drivers), or disable the nVidia in Device Manager, forcing it to use only the Intel HD Graphics. Edited, Sep 16th 2011 12:01am by BDHERTZER Edited, Sep 16th 2011 12:11am by BDHERTZER