Time: 2am GMT+1
Frequency: Very often
World name: Shiva
Character name: Baal Mirtaq
NPC name: -
Monster name: Demon Wall
Class/Level: Dragoon 50
Party or solo: Party, 4 players
In-game time: -
Area: Amdapor Keep
Steps:
1. The boss battle started
2. Demon Wall was not targetable through normal means (using the directional buttons or pressing R2/L2+R1/L1)

Model Number of the PlayStation 3 You Are Using
- Model Number: PS3 slim CECH-2504B

The glitch can be circumvented by going into mouse mode and clicking on demon wall or alternatively having a PC player with you and using an assist macro. The other PS3 players in my group had the same issues.
In very rare occasions the last boss in amdpor keep would not be targetable as well.