try pulling your card out and then put it back in. sometimes it gets loose. and where does it say that? in recovery or when booted up?
Tried that multiple times. I did a google search for the solution and was led to xda-developers site.
It said that this sometimes happens when the cache are wiped. You have to go back in, go to fast boot and type in a command to remount via adp ( i think that's right), but you need the Android SDK which i can't find on my phone in fastboot or recovery.
I'm probably overlooking it, but no luck as of yet.
Jaz