Zone transfer fails - "connection refused"

[Jan Ole Kastens]

Hi list !

I maintain several named's of the same version (4.9.7-57). Theese named's
provide DNS over a dialup network.
Each server has every other server on the dialup network as secondary in the
named.boot.
Everything worked fine until one of the named's started to make truble:

Evevery zone transfer from that name server now fails with the message
"Error getting serial for "zone" ... " and
a message by the zone transfer process "Connection refused".

Every named is providing DNS for his LAN and the named making trouble is
working fine in all other cases.
The dialup connection is tested and ok.

What can be the reason for such a failure ?

Greetings

Jan Ole Kastens