Headers already sent in Debug

[incircolo]

I have a lot of the following message in debug file
PHP Warning: Cannot modify header information - headers already sent in Unknown on line 0

version 1.3.9h

Why is not a file defined and i see "Unknown" ?

PS.
It is an admin related warning

[wmorris]

Did it show which file has been sent? Mostly its to do with the end of a file that ends with ?> with spaces after.

here is an article to help you solve your problem.

https://www.zen-cart.com/tutorials/index.php?article=87

[incircolo]

Thanks
I've already read it.
The problem is that there is no file, but "Unknown on line 0"

[DrByte]

When did this suddenly start happening? How might that be significant?

"Unknown on line 0" is used whenever the PHP engine is encountering a problem that's triggered by something for which it can't identify the filename. That might be a server configuration issue, or a compiled PHP library component. Those would be things your host would have to fix.
It might be triggered by using encrypted or encoded PHP scripts / addons. So, if you've added one of those recently then you'll need to sort that problem out with the author you purchased the addon from.

It might not (and quite likely does not) have nothing to with Zen Cart core code at all. If it's caused by files added to your Zen Cart files/folders, either by you or maliciously by an intruder, you can at least check to see whether something unexpected exists by doing a comparison: http://www.zen-cart.com/wiki/index.p...Obscure_Issues

And if you do find stuff on your server that you didn't put there or don't expect to see there, then you should really inspect everything thoroughly: http://www.zen-cart.com/wiki/index.p...ing_From_Hacks

You may find it necessary to engage your hosting company to determine the actual cause of the error.