Same problem here. I've checked the right, they're ok, I've emailed my host (GoDaddy) and here is answer - seems to me they have no idea, what I want them to do. I have access to php.ini, would that be helpful?
My host response:
Thank you for contacting Online Support. It is my understanding you are having trouble with your website. This error is caused if the your PHP scripts are printing to the browser prior to sending headers. A common example is printing the html tags prior to starting a session, or setting a cookie. The error tells the line that needs to be altered. To resolve this error remove the lines from the PHP code that are printing to the browser prior to sending headers.
Please let us know if you have any further questions, comments, or concerns. Our service departments and telephone lines are open 24 hours a day, 365 days a year to accommodate your needs anytime.
You can reach us by phone at any time at (480) 505-8877, or simply reply to this email.
Please let us know if we can assist you in any other way.
Sincerely,
Anna P.
Online Support Team