Error about love upset miss having egotistical attitude (9)
I believe the answer is:
solipsism
'egotistical attitude' is the definition.
(belief that only one's self exists)
'error about love upset miss' is the wordplay.
'error' becomes 'slip' (slip is a kind of error).
'about' means one lot of letters goes inside another.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'upset' indicates anagramming the letters.
'slip' going around 'o' is 'solip'.
'miss' is an anagram of 'sism'.
'solip'+'sism'='SOLIPSISM'
'having' is the link.
(Other definitions for solipsism that I've seen before include "egotistic attitude" , "Selfishness" , "self-centredness" , "Sort of philosophy" .)