Thoth "unsup****ted header" field

I've been attempting to transition from my previous ISP's news server
to my new one's (comcast). I use Thoth. For the comp.sys.mac.system
group, I now get an error on an attempted open. The Thoth log file
re****ts an "unsup****ted header" field. 

If I read the log correctly, it is objecting to "XHDR NNTP-Posting-Host
732925-732935". Shouldn't the server itself be filtering out such a
message if indeed it has an invalid header. Of course, I can't do
anything about any messages in a group that have invalid parts. Do any
of you know what this is really about? Is this likely a Thoth problem
or a newsgroups.comcast.net problem? Up until today, I could read the
same group from *.rr.com (roadrunner), but now that newserver re****ts
that "access is denied to your node". I sure am use to Thoth. Any help
with this would be appreciated.