That error is just telling you that there was no buffer to delete.
To avoid it just use:
if (ob_get_contents()) ob_end_clean();
(check if there’s an active output buffer)
or:
if (ob_get_length()) ob_end_clean();
(checks if there’s a non empty string in the buffer)
as suggested by @Venu.
also you are calling ob_end_clean(); two times there. And that only works with stackable buffers. From the PHP manual:
This function discards the contents of the topmost output buffer and
turns off this output buffering.
Are you sure you don’t want to just use ob_clean()?