upgrad to 1.7.6.0 with fatal error

[Fredy Kunz]

got in the upgrad process en error in the currency modul:

[INTERNAL] /home/httpd/vhosts/chumm-ine.ch/httpdocs/presta/admin026rcnyfg/autoupgrade/latest/install/upgrade/php/ps_1760_copy_data_from_currency_to_currency_lang.php line 55 - Call to a member function get() on null

Can I delete or prepare the old version to upgrade it. Then the rollback has give also en error.- so that I stand at moment without shop: 

[INTERNAL] /home/httpd/vhosts/chumm-ine.ch/httpdocs/presta/config/config.inc.php line 121 - Call to a member function getName() on null

Have thanks for help