Parked Domain And Mx Entry Can we change parked domains mx entries

I assigned an uni.cc domain as a parked domain in my account and i'm willing to change its mx records so it will point to google mx records. But I always get an error message everytime i try it. I didn't have any problem before when I changed mx records in my domain (the real and addon ones).Is it able to change mx records in parked domain? Or, is there any way to solve this problem?