What Mismatch ID error means ?

Hi,

Occasionally, I will encounter the following error:

6/15/07 12:11:46 PM (Version 0.14.6.447 (Beta)): Message-ID mismatch! 
Server="RCN", Group="some_group_name", Response="220 
22876300 <[email protected]>", 
requested "<...>".

What does this error mean ?  This problem usually goes away when I 
unmark this article from the download queue; refresh the group and then 
re-mark the article for download.  The download again will be 
successful (otherwise I believe BNR will keep retrying the 
article ???).  Why does it happen ?  Any way to fix or avoid the 
problem ?

.......



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