Raise the DFL and FFL after the migrate domain from 2003 to 2012 r2 getting error

we are facing a issue while the raise the DFL and FFL  . we are getting the error"you cannot raise the domain functional level because this domain includes active directory domain are not running appropriate version of windows" .we have  migrate all FSMO role from 2003 to 2012  but in this time windows 2012 and 2003 run together, windows 2012 act as PDC and Windows 2003 ac as  ADC . please suggest to step by step how to raised the  level.