Calling hook CanUseLockedEntity resulted in a conflict
Calling hook CanUseLockedEntity resulted in a conflict between the following plugins: Vanish - False (Boolean), MasterKey (True (Boolean))

Merged post

Also noticed vanish doesn't always work how it should. Turrets are shooting me sometimes while vanished (not always, but when it does the vanish pictogram left-down is gone but vanish enabled) and npc's where still able to see me and shoot me while vanished.
"Calling hook CanUseLockedEntity resulted in a conflict between the following plugins: Vanish - False (Boolean), MasterKey (True Boolean))"

The issue would be how Vanish handles the player than something with the Master Key plugin.
The warning is telling you that there is a potential conflict there. If everything works fine, you can safetly ignore it. In this case, the only "conflict" would be that one is denying access and one is allowing, but only one result will work.
I was referring to your words posted on the Master Key's forum. This conflict is not an issue with Masterkey either?
In response to y88cdw ():
I was referring to your words posted on the Master Key's forum. This conflict is not an issue with M...
This warning and something breaking aren't necessarily related. In this case, the hook warning is telling you what I mentioned above. There isn't really anything that can be done to make a door open if the door has already been told not to by another plugin, but if you are seeing actual errors or other odd messages, then it is likely unrelated to this hook warning and the actual hook result as I mentioned in the other thread.

Also, I posted in the other thread to you, same Wulf. ;)
The hook notice doesn't show in console if Vanish is deactivated, and the Masterkey plugin works only in that condition.

The master key plugin is not working if vanish is activated.
In response to y88cdw ():
The hook notice doesn't show in console if Vanish is deactivated, and the Masterkey plugin works onl...
Right, because the conflict wouldn't exist and hence no warning when one of the parties involved is not there. You can't really tell a player to do opposite things and expect it to work, hence the warning.
As this is turning out to be feature request rather than bug, I would politely ask his developer if such an option could ever allow in config to open an owned locked door (and by extension the use of Master Key plugin) while being vanished. It would be a very welcome tool for admins.