an unknown error occured while attempting to perform this command

Thank you for your report.
However, your ticket has been resolved as awaiting response.

We currently do not have enough information to troubleshoot your issue.
Please force a crash by pressing F3 + C for 10 seconds while in-game and attach the crash report ([minecraft/crash-reports/crash-<DATE>-client.txt|http://hopper.minecraft.net/help/finding-minecraft-data-folder]) here.

Your report will be reopened or properly resolved as soon as we receive this information.

I have the crash report attached.

Your crash report indicates that cheats are not enabled in that world, which would prevent that command from running. However, I get the message "You do not have permission to use this command", rather than "an unknown error occured while attempting to perform this command". Could you try the same command in a world that has cheats enabled?

I have tried it in a world that has cheats enabled and it worked. But the world which I got the error in said that cheats were enabled. I have a feeling it could relate to MC-87504 because this issue and the other occurred in the same world.

So did you generate that crash report in the same world where you were experiencing these issues, or in a different world?

@Torabi Client crash reports don't have access to the world settings (seed, level storage version, rain/thunder time, hardcore and cheats options).

@ Reporter Attach the game output from when you got the error message.

Does the issue still exist in 15w44b? If so, please attach the game output, like @unknown asked.

Ticket resolved as incomplete, because no answer in a reasonable amount of time (1+ year), if it still happens, please update the ticket.