Got messages on the Emirates app, website, e-mail, etc. telling me that I can check-in online but, when I go to do so, I get:

"Sorry, you can’t check in online as you're either connecting from another flight or another airline, or your flight is not currently open for check-in. Please check in at the airport or try again later."

Flying in F from HKG to DXB, then DXB to MAN, all on one booking and all with EK.

Any clue why I'm getting the above message?