Basecamp & Garmin 276Cx Coordinates

Can anyone help please as I must be doing something wrong.

My garmin is connected to my macbook 

I live in the UK

I have Topo GB Pro 1:50k installed.

Question, I can't find a grid reference when a go to , find, locate Coordinates 

Anything I type it says invalid coordinates as soon as I enter the first digit or number.

NY 385 466

338500 546600

54.810471 -2.9584160

Must have settings wrong somewhere. 

Any help appreciated