You have several places that templates exist in LedgerSMB

/var/lib/ledgersmb/css/ for the LedgerSMB user interface templates
and
/usr/share/ledgersmb/templates/demo for the Latex / HTML report output templates.

Run the following commands as root (or sudo command):
chown www-data:www-data /var/lib/ledgersmb/css/ -Rv
chown www-data:www-data /usr/share/ledgersmb/templates/demo -Rv