2 servers won't sync browse lists accross network

[Greg Patten]

We've got two samba servers either side of a modem link and I'm trying
to get them to sync browse lists. Using remote sync and friends the
servers try and sync but invariably each time one does the other end
rejects the `browse sync sessionsetup' i.e.

sync_with_lmb: Initiating sync with local master browser BOX1<0x20> at
IP 192.168.1.2 for workgroup WORKGROUP
04/06/1998 21:44:53: sync_browse_lists: Sync browse lists with server BOX1<20> a
t IP 192.168.1.2 for workgroup WORKGROUP
Connecting to 192.168.1.2 at port 139
sync_browse_lists: BOX1 rejected the browse sync sessionsetup

Can someone tell me what this might be and how I can avoid it. I've
followed BROWSING.txt to the letter (as far as I can tell). i.e. one
domain master, both servers are local masters, one wins server etc.

I'm sure I must be missing something simple ..

Cheers and many thanks in advance,
Greg.

PS. Please CC response if possible.