Define Instrument not enabled

[Roy Slough]

I use define instrument to make midi entry easier when using Ample Guitars - It allows changes to the note names shown on the piano keys in piano roll view.

I wanted to update some of my previous entries to allow for new things I discovered (Silent press etc..)  However, the define instrument button is not enabled in the preferences/Midi Instrument section (see screenshot) You can see I have previously defined entries for Ample Guitar non strumming and strumming modes

I cannot think what I am doing differently or wrong since I last entered some values.
The only thing I have done is install the latest patch upgrade (Version 2024.12) Could this have affected this?

Any advice please. I can continue without this but it does make things easier.

[User 905133]

Do you have any midi outputs selected [MIDI Devices]?

PS: As an alternative for the time being would you be comfortable editing copies of the older instrument definitions in Notepad?

Edited 3 hours ago by User 905133
to add a PS