EXP 50 Can't Program Speed Dial DSSKEY

[Qbart]

Hello,

I'm using a Yealink T58A phone with the EXP 50 module. I can program all the expansion module DSSkeys except for one. The number 14 key. It used to have a speed dial number attached but it was deleted. Now when I try to reprogram it, I hold it down and it lights up for a few seconds, but nothing happens. I don't get the screen on the phone to be able to program it. I can program every other key but that one. Does anyone know what could be the problem and how to solve it?

Thanks in advance.