mails are not beeing send (on action and cron triggered)

When subscribing to forum post following errors are seen in watchdog log:

Missing argument 3 for subscriptions_comment_page() w pliku xxx/modules/subscriptions/subscriptions.module, linia 633.

error mailing subscription notification: "xxxx"

Tested both on cron and on action settings.
Environment as follow:

**********************
Drupal 5.1
Configuration file Protected
Cron maintenance tasks Last run 1 min 43 sec ago
You can run cron manually.
Database schema Up to date
File system Writable (private download method)
MySQL database 4.1.21
PHP 4.4.4
Unicode library PHP Mbstring Extension
Web server Apache/1.3.37 (Unix) mod_fastcgi/2.4.2 mod_auth_passthrough/1.8 mod_log_bytes/1.2 mod_bwlimited/1.4 FrontPage/5.0.2.2635.SR1.2 mod_ssl/2.8.28 OpenSSL/0.9.7a PHP-CGI/0.1b
***************

Mails from system (like passwords, registrations and so on) are delivered smoothly. I simply don't know what to think about it (pretty unbelievable that main functionality is not working ....)
Any ideas?