Possible Bug Causing Random Game Crashes White Using Trust Alter Ego's.

Platform: Windows 10 PC
ISP: Virgin Media
Type of Internet Connection: Broadband
Internet Connection Speed: 500Mbps
Date & Time: July 12 2020, 22:00 GMT
Frequency: Sometimes
Character Name: Ireland
Race: Hume Male
World: Cerberus
Main Job: Black Mage Level 99
Support Job: White Mage Level 49
Area and Coordinates: Abyssea - La Theine, H-7
Party or Solo: Solo (using 5 Trust alter ego's)
NPC Name: None
Monster Name: Baba Yaga
Steps:

I reported the above problem to a GM and he directed me here. Sometimes when I have trust alter ego's out, the game will crash after using weaponskills and/or casting spells. Problem started a few weeks ago fighting Apex Bats on White Mage 99 in Dho Gates while using full Trust alter ego party. The game would crash on a few occasions with the following message:

"Terminated as error occurred in FINAL FANTASY XI. Full-screen mode was lost.(-1)"

I am not using any third party programs or any modifications of any kind.

This has only started happening in the last few weeks. Sometimes it happens 2 or 3 times per session, but only seems to happen while using weaponskills and/or casting spells. Sometimes it does not happen at all, but on another occasion in Dho Gates on White Mage 99 it happened about 10 times in the one night.

I can do things with my character without any problems usually, but if it involves using weaponskills and/or spells it can trigger again. I even finished Rhapsodies Of Vana'diel as some of the trust alter ego's are blocked and unobtainable until you clear certain missions, and I thought that it was possibly something to do with this that was causing the crashes.

Even as I write this, my character is in Port Jeuno for some time and the game is playing away in the background without any problem. If I take my character somewhere to fight it can trigger this strange bug. I fought Fenrir again in a quest and it happened there, and while fighting Bahamut during Storms Of Fate it crashed while casting spells. This seems to be totally random, and only while trust are present. I may get lucky and have no issue with it during a session, but lately it happens about 1 or 2 times during gameplay and it can be annoying.

Hopefully somebody can give me some information or help with this matter, as it only started happening a few weeks ago and before that I never had any issues with the game at all. I play Final Fantasy XIV on the same computer and I have no problems with that at all.

Any help would be appreciated. Thank You.

Sounds like something on your PC is grabbing focus from FFXI, causing that error. You could be hitting the windows key, or some key combination that forces the game to minimize, which the game can't handle if you don't have windowed or border-less full-screen mode enabled.