Kindly Uninstall and re-install the Prestashop CMS or do a fresh installation of Prestashop on a sub-domain and then install the VoguePay Plugin to test as we have tested on our test platform and did not encounter the issue you encountered.
Also, Since you do not have a account on VoguePay, kindly use "demo" as your merchant id which will be needed in setting up the plugin.
Regards.