PHP Error with Download helper & a model

[eluser]russ_kern[/eluser]
Wondering if I could get some advice... I have a page that allows for the CSV export of data... in loading the Download helper, I get this error:

"A PHP Error was encountered

Severity: Warning

Message: Cannot modify header information - headers already sent by (output started at /home/xxxxxxx/public_html/system/application/models/functions_model.php:341)

Filename: helpers/download_helper.php

Line Number: 86"

I get this error repeating for any line in the download helper that has a header() call. I know the error is some thing silly in my functions_model, but I have combed through it and can't find it. I do not have any header calls in the functions_model, and as line "341" is the last line of the functions_model, it must be a missplaced space or something... can anyone point out the sorts of things that would cause this? After spending and hour or two I'm stumped... Any help would be great.

Thanks. Russ