I just went through this on the '05 ST I just bought. I found 2 'fixes' online. The first was about pulling the fuses, the other was to press the 3 & 6 buttons while the radio is on & in FM1 mode. This puts the radio in a test mode & should clear some errors. After letting it run through test mode turn truck off & open door (turn radio off completely) for about a minute, you may have to do this a few times. I ended up running the test mode a few times=didn't fix it, then pulled fuses=didn't fix it, ran test mode a couple more times & it worked. You'll probably know right away when you turn the radio on if it worked because if it's going to give the eject error you'll hear a whirring sound for about 30 seconds when the radio first comes on. If you've cleared the error you shouldn't hear that noise.
My project now for my radio is that someone before me replaced the stock '05 radio with a '07/'08 model Ford radio with an AUX button/input. Only problem is they didn't install the wire/jack to allow use of this feature so I have to try to find that wire/plug somewhere & install it. I'm thinking maybe a junkyard & look at some late model Explorers?