gnus `unknown option -dump'

[nickname]

Hello,

I've been using gnus for a few months already, though I only use it
for personal and business mail .

Yesterday, when trying to access to my particular folder, I was
prompted with something like: "how many messages to show (210):", to
which I just pressed enter.

>From there on, some of the last messages received just display the
message "Unknown option -dump" in the body, while the file in the disk
retain it's original content.

Replying to those emails, also result in just that message being on
it.

I did set `gnus-large-newsgroup' to 300, but still this happens. It
seems to be somewhat random, though. It doesn't happen to all the
messages in that group.

Does somebody know what I coul do about this? I'm using `GNU Emacs
23.1.50.1 (i686-pc-linux-gnu) of 2009-10-18.

Regards,