Prueba cambianado está opción de tu php.ini
Yo tuve un problema similar con una estadistica que estaba desarrollando ;)
;;;;;;;;;;;;;;;;;;;;
; Language Options ;
;;;;;;;;;;;;;;;;;;;;
; Output buffering allows you to send header lines (including cookies) even
; after you send body content, at the price of slowing PHP's output layer a
; bit. You can enable output buffering during runtime by calling the output
; buffering functions. You can also enable output buffering for all files by
; setting this directive to On. If you wish to limit the size of the buffer
; to a certain size - you can use a maximum number of bytes instead of 'On', as
; a value for this directive (e.g., output_buffering=4096).
output_buffering = 4096
Suerte y saludos.