UPB Links not working

I have been using MisterHouse to control devices for a little while and it works beautifully.
What I can't seem to implement though are Links.
I have in my items.mht file:
     UPBL,a1001,pim1,250,6
Obviously the pim, pim1, is working as it can correctly control lights.
My Network ID is 250.
The Link ID is 6.
When I type the following into the mh external prompt:
     set $a1001 'on'
mh accepts the command, the PIM buzzes as it does when transmitting,
but the set of 2 switches in my kitchen do not turn on.
Does anyone have any idea what my be going wrong?
I'd be more than happy to supply information towards figuring this out.