$html=$this->load->view('r2013ms/Long_term_agreement',$data);
$obj_pdf->writeHTML($html);
$obj_pdf->Output('Agree.pdf', 'I');
Severity: Notice
Message: Undefined offset: 0
Filename: tcpdf/tcpdf.php
Line Number: 17155
A PHP Error was encountered
Severity: Notice
Message: Undefined offset: 0
Filename: tcpdf/tcpdf.php
Line Number: 17522
TCPDF ERROR: Some data has already been output, can't send PDF file
When you have "TCPDF ERROR: Some data has already been output, can't send PDF file" it's because you have displayed something in screen. Maybe another warning.
Try to put an "@" before the function's call, that will supress the error message source
if all works fine, you know where search the error