I'm up pole in error (7)
I believe the answer is:
mistake
'error' is the definition.
('mistake' can be a synonym of 'error')
'i'm up pole' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'pole' becomes 'stake' (I've seen this before).
'im' reversed gives 'mi'.
'mi'+'stake'='MISTAKE'
'in' acts as a link.
(Other definitions for mistake that I've seen before include "16 down" , "Oversight" , "Slip" , "Error" , "Wrong action or judgment" .)