Server cannot set content type after HTTP headers have been sent

[DISP Jol]

Hi folks, I have to generate a PDF on a webpage which takes long time to load... I am using a progress bar web custom control on this page to indicate progress... But I get the error message "Server cannot set content type after HTTP headers have been sent".... Without the progress bar the page just loads up fine... Any ideas to get this resolved... Thanks Joel

JO