congratulations!
You have been specially selected for an "enhanced" screening at the checkpoint. If your gate is "randomly" selected for additional screening, you also get to go through the 'gaterape' sequence.

I think they are starting to deny internet checkin to 'selectees' because they might have discovered the easy way to get out of "enhanced" screening was to "liquid-paper out" out the "SSSS" or "SELPAX" code on the boarding card, and then run it through the photocopier (I take the 5th on that one). This way you are forced to check in at the airport and get a boarding card with the screening tag on it for sure.

If you dont mind, post the results of your check-in experience so we know for sure what the real consequences of that message are.