Can somebody please tell me my translation is wrong, because this is jibberish to me. First there are puellae as confirmed by ferunt but then there is only one, as shown by soluit !!
I am most confused… 
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.
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.
Thanks Benissimus, most helpful as always!!
Nice idea, although probably not intended, that fers 
, the Apple of Discord is the one that unties the girdle 
.
Rather than the Apple of Discord, how about the golden apple which led to Atalanta’s marriage to Hippomenes?
Magistra