A muddle as I object to the cat climbing (4-2)
I believe the answer is:
mess-up
'a muddle' is the definition.
(I've seen this before)
'i object to the cat climbing' is the wordplay.
'i object' becomes 'me' ().
'to the cat' becomes 'puss' (puss is a kind of cat).
'climbing' says the letters should be written in reverse (in a down clue, letters climb up).
'puss' written backwards gives 'ssup'.
'me'+'ssup'='MESS-UP'
'as' acts as a link.
(Other definitions for mess-up that I've seen before include "Muddle, bungle" , "Handle (something) ineptly" , "Muddle - confusion" , "Ruin" , "Fiasco" .)