Hello, 

After insatlling wkhtmltopdf on my server and get the following error msg when i try to print a pdf :

 Odoo Server Error
Traceback (most recent call last):

File "/opt/odoo/odoo9/addons/report/controllers/main.py", line 96, in report_download
response = self.report_routes(reportname, docids=docids, converter='pdf')
File "/opt/odoo/odoo9/openerp/http.py", line 512, in response_wrap
response = f(*args, **kw)
File "/opt/odoo/odoo9/addons/report/controllers/main.py", line 45, in report_routes
pdf = report_obj.get_pdf(cr, uid, docids, reportname, data=data, context=context)
File "/opt/odoo/odoo9/openerp/api.py", line 250, in wrapper
return old_api(self, *args, **kwargs)
File "/opt/odoo/odoo9/addons/report/models/report.py", line 182, in get_pdf
save_in_attachment = self._check_attachment_use(cr, uid, ids, report)
File "/opt/odoo/odoo9/openerp/api.py", line 250, in wrapper
return old_api(self, *args, **kwargs)
File "/opt/odoo/odoo9/addons/report/models/report.py", line 324, in _check_attachment_use
pdf = base64.decodestring(pdf)
File "/usr/lib/python2.7/base64.py", line 321, in decodestring
return binascii.a2b_base64(s)
TypeError: must be string or buffer, not None

Many thanks