Error some puppets simply sent up (7)
I believe the answer is:
misstep
'error' is the definition.
(misstep can mean an error or mistake)
'some puppets simply sent up' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'sent up' shows that the letters should be reversed in order.
'petssim' is hidden in the letters of 'puppets simply'.
'petssim' written backwards gives 'MISSTEP'.
(Other definitions for misstep that I've seen before include "Badly judged move" , "False move" , "Badly judged footing" , "bad move" , "Error" .)