Hi there, and welcome to Beoworld.
I'm sorry no-one has got back to you before now. I guess it is because it is unusual to have Beocom 1 and 600s mixed.
As far as I am aware, they are identical, but named differently for different markets.
Check that there are not any other handsets registered to your base, it can only handle 6 handsets.
Try 'removing' all handsets except the one you use, then try adding your Beocom 1.
Get back to us if you need more help.
Andy T.