The most common and most likely answer to this crossword clue is the 12 letter word MISATTRIBUTE
M
I
S
A
T
T
R
I
B
U
T
E
Buddy explains!
The straight part
We know that "Put down in error" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case put down in error = misattribute.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MISATTRIBUTE mean?
MISATTRIBUTE verb- To erroneously attribute; to falsely ascribe; used especially of authorship.