Changing settings gives PHP error

Hi there,

Thanks for bringing this up, I have tried to replicate but have been unable to.

This message indicates that somewhere on your installation a php file outputs headers before its time.
You can solve this issue by following the process below:
Switch your theme to the default twentytwelve theme and deactivate all other plugins except the Smush.it plugin.
You should now see that this error no longer exists.
To find out which plugin/theme triggers this issue, start activating them one-by-one and test again.
Finally, activate your previously selected theme.

Next, you’ll have to inspect the files of the plugin that triggers this error.

Open all php files one by one and check for the following:

If there is a space or blank line before the opening <?php tag on the file, delete those spaces or lines.

If there is a closing ?> tag at the end of the file, delete it.

As stated in the PHP docs,

The closing tag of a PHP block at the end of a file is optional, and in some cases omitting it is helpful when using include or require, so unwanted whitespace will not occur at the end of files, and you will still be able to add headers to the response later. It is also handy if you use output buffering, and would not like to see added unwanted whitespace at the end of the parts generated by the included files.

Please advise, if this fixes the issue.

Thank you!

Kind Regards
Jack.