slow SSD speed with Dual Hard Drive Kit

I just installed a Crucial C300 in my mac mini using the Mac Mini Dual Hard Drive Kit.

While cloning the HDD to the SSD using CarbonCopyCloner (which I've used successfully multiple times on a MacBookPro and a MacPro), the SSD suddenly disappeared and won't show until a 10 minutes "cooldown".

I then tried to copy 4Go files to the SSD from the HDD, and every 10 seconds the copy stalls for 30 seconds.

Can it be a faulty cable? or is it a Sata speed issue (as seen on some MacbookPro using 3G data SSD)?

EDIT: I've tried with another SSD (a Crucial M4 and a Samsung 840) , and it worked perfectly. So it seems that the Crucial C300 is not "supported"