Nokia released New Security SL3 With New Firmwares .
it can't be downgrade, unlock ,OR use RPL

IF YOU TRY WRITE RPL TO THIS MODELS YOU MAY SEE THIS FAULTS :
* white blinking
* Contact Service
* NOKIA logo freeze
* Security 'Failed to Read'
* dead handset
* damaged IMEI - 12345678901?

MODELS WITH NEW SECURITY :
* 5310 MCU v58.58, v59.42 (RM-303)
* 6300 MCU v57.20 (RM-217)
* 6500c MCU v59.45 (RM-265)
* 6500s MCU v59.60 (RM-240)

New Security phones, not included new Frimwares,
based on RAP3GS_V3.02-PA_SL2 CPU
* 6600 fold (RM-325)
* 6600 slide (RM-414)

based on RAPS_V3.03-PA_SL2 CPU
* 3600 slide (RM-352)
* 5220 XpressMusic (RM-410/RM411)
* 7210 Supernova (RM-436)
* 7310 Supernova (RM-378/RM-379)
* 7610 Supernova (RM-354)

And ANOTHER information about SL3 click here

Also check here, for another information