Activation of Terms of Use make path user/register unavailable with error

Dear all,

i got the following error on page user/register after activation of the module.

Fatal error: Call to undefined function i18nstrings() in /var/www/synertal.dnsalias.net/htdocs/mycontemporary-sandbox/sites/all/modules/terms_of_use/terms_of_use.module on line 283

if i inactivate it, user/register is available again. what is the problem?