Please enter the number from which you are calling

Ran into an issue this morning- have an extension- just one, that is acting differently than the rest. Anyone who calls it from any extension in the org gets a message saying "Please enter the number from which you are calling, followed by the pound key" No matter what we enter (our extension, our full phone number, her ext) the call gets rejected. But really, I don't care what the right input is, I don't want it asking this question at all, I just want it to ring as intended when someone calls her.

Of course, when I called support, they were clueless, walked me through the sort of things every IT guy would already have done- rebooting the phone, power-down and reboot phone, they even had me move it to another cat5 plug, as though it's the frikking plug that changed the setting....) So I'm turning to here hoping someone has run across this issue before. 

Thanks!