Kasper wrote:First there are puellae as confirmed by ferunt but then there is only one, as shown by soluit !!
So it would seem, but
puellae is actually a dative in agreement with
pernici.
pernici cannot be a nominative plural as you have it (
pernix, -icis). The
implied subject of
solvit is
puella, though.
Tam gratum est mihi quam ferunt puellae
pernici aureolum fuisse malum,
quod zonam soluit diu ligatam.
So pleasing it is to me
to have been the golden apple which the swift girls carry
because too long she used the girdle which was tied.
There is a
tam... quam... idiom here: "as.... as..." (literally "how much... how...").
quam therefore is a conjunction, and even if it were a feminine relative it could not refer to the neuter
malum.
ferunt can mean "they carry", but here it means "they say", which is a common meaning of the word. Compare with English "to carry on (about something)".
aureolum fuisse malum then becomes clear as an indirect statement following a verb of saying.
solvit means "loosened", not "used".
diu is probably modifying
ligatam, not
soluit.
I have to say, I was still a little confused after I read it. I believe it is a reference to the Apple of Discord. What is "
tam gratum" to Catullus, and how the poem relates to the other Catullus II is unknown to me. If you still have trouble with it or just want to compare, I will give my translation.
flebile nescio quid queritur lyra, flebile lingua murmurat exanimis, respondent flebile ripae
, the Apple of Discord is the one that unties the girdle 
.