[Posting on behalf of a sprout friend, who's not on the forums.]

They started the MSQ quest The Ultimate Weapon after the 6.1 maintenance. After reaching the step "Confront Lahabrea on the Porta Decumana.", you are supposed to fight Lahabrea in a solo duty.

Starting this solo duty is impossible. After the cutscene plays, the duty does not start, and "A system error occurred during event movement." is printed in chat. This error implies this is a serverside issue, and not an issue with client integrity.

Abandoning the quest is not possible - therefore this softlocks the MSQ. They submitted a bug report using the in-game Support Desk but after a few days no reply has come.

Things they have tried:
- Restarting game
- Restarting PC
- Exiting and entering the area
- Waiting for the cutscene to play out in full
- Using the World Visit System to attempt the duty on another world
- Abandoning the quest (not available)

Date & Time: After Patch 6.1
Frequency: All
World name: Gilgamesh
Character name: Nyaku Astaze
Retainer name: N/A
NPC name: Lahabrea
Monster name: N/A
Class/Level: PLD, 50
Party or solo: Solo
In-game time: N/A
Area and coordinates: The Porta Decumana (world area reached by using the passage next to The Praetorium's entrance - not the trial!)
Housing: N/A
Steps:
1. Accept the quest "The Ultimate Weapon" after Patch 6.1
2. Reach the quest step "Confront Lahabrea on the Porta Decumana."
3. Speak with Lahabrea to start the solo duty
4. Notice how the solo duty does not start