Warning: preg_replace_callback() [function.preg-replace-callback]: Requires argument 2

When installing the module and sent a test newsletter I receive the following error Warning: preg_replace_callback() [function.preg-replace-callback]: Requires argument 2, '', to be a valid callback in _simplenews_statistics_parse_links() (line 248 of /var/clients/clientx/weby/web/sites/all/modules/simplenews_statistics/simplenews_statistics.module)."

Any ideas? Thanks in advance!

Error occours within alpha version as well..
[PHP 5.3.2, webserver Apache]