Its happened to me a number of times with OE and Individual.net. I found
the only way to fix it was to start a new thread with same subject line
and paste in the bit I was replying to.

"Julie Bove" > wrote in message
...
> This is frustrating! Sometimes I can reply in the Ellen's breakfast
> thread and it works. Other times I can not reply. I am getting an
> error message that the header is too long. Shortening the header does
> no good either. So I don't know what the problem is. But it's
> probably with Eternal September.
>