Panic about count I ran perversely having mistake in the maths (10,5)

I believe the answer is:

truncation error

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'mistake in the maths' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'panic about count i ran perversely' is the wordplay.
'panic' becomes 'terror' (synonyms).
'about' is an insertion indicator.
'perversely' is an anagram indicator.
'count'+'i'+'ran'='countiran'
'countiran' is an anagram of 'runcation'.
'terror' placed around 'runcation' is 'TRUNCATION ERROR'.

'having' is the link.

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