If you use /effect and set the id value to be greater than 31 instead of displaying "There is no such mob effect with that id" it displays the internal error message that means the command has generally broken.

See attachment (the outputs are from me trying numbers 30 to 33. I have also tried this with 43 (i was entering random numbers as parameters when I tried this)

The exact command I ran was " /effect @p 33 " in case it is something else causing the message.