Foolish error following American in Spain (7)
I believe the answer is:
asinine
'foolish' is the definition.
('asinine' can be similar in meaning to 'foolish')
'error following american in spain' is the wordplay.
'error' becomes 'sin' (I've seen this in other clues**).
'following' is a charade indicator (letters next to each other).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'spain' becomes 'e' (abbreviation for Espana).
'sin' put after 'a' is 'asin'.
'asin'+'in'+'e'='ASININE'
(Other definitions for asinine that I've seen before include "Senseless" , "Jenny's often like this" , "Absurd" , "Is inane to be foolish" , "Stupid (as a donkey?)" .)