Make a mistake with task involving travel (6)
I believe the answer is:
errand
'task involving travel' is the definition.
(an errand is a task requiring you to travel)
'make a mistake with' is the wordplay.
'make a mistake' becomes 'err' (to err is to make an error).
'with' becomes 'and'.
'err'+'and'='ERRAND'
(Other definitions for errand that I've seen before include "Job usually involving a short trip" , "Messenger's job" , "Useful journey" , "In purposeful trip" , "Message run" .)