New butler admitting old problem (7)
I believe the answer is:
trouble
'problem' is the definition.
('trouble' can be a synonym of 'problem')
'new butler admitting old' is the wordplay.
'new' indicates anagramming the letters.
'admitting' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'butler' with letters rearranged gives 'truble'.
'truble' going around 'o' is 'TROUBLE'.
(Other definitions for trouble that I've seen before include "Hassle" , "'Care, distress (7)'" , "Conflict" , "Nuisance, bother" , "Worry - predicament" .)