Why isn't my apple ID working when I try to activate my iPhone 5c after 9.3 update?

My iPhone 5c asked me to update the software like usual when a new update rolls along, and I followed through as soon as I saw it. It says it updated successfully and all I have to do is activate it, asking me to enter my apple ID and password. I did, but it won't allow me, saying that this apple ID cannot be used to unlock my phone. I know for sure that I am typing the apple ID correctly as well as the password, because I tried signing into iTunes and iCloud on my iMac and it works. For some reason, it will not allow me to activate my iPhone with the same apple ID.

HELP!