Upgrading Drupal

I am trying to update to the latest Drupal from a previous 6.x install. The update goes ok until it gets to the last step. When it accesses:

http://[snip]/update.php?id=3&op=finished

It throws the following error:

Fatal error: Cannot pass parameter 4 by reference in /home/gorf/public_html/[snip]/www/modules/user/user.module on line 1955

I don't seem to be able to get it to do anything but throw this fatal error.

I am running Apache 2.2 on CentOS 5 (i386) with PHP 5.3.1.

Except for in Firefox 3.5.6 in Linux. That is the only browser & O/S combo that is still displaying Events. I updated to 6.15 from 6.14 on23 Jan. On 25 Jan., the fellow in charge of creating events on our site informed me that he cannot create events because the fields no longer display on the Create Content page, and that Calendar items are not displaying. This is in Windows, IE7. It works for me in Firefox 3.5.6 in Linux. No other browser - O/S combo will display the content.

I have download Security update: 6.15 (2009-Dec-16) , but I dont know where to put it or how to install it , can someone help me step by step , ty

Upgrading causes this error:

    * Notice: Undefined index: module in _field_info_prepare_instance_display() (line 323 of /var/www/../modules/field/field.info.inc).
    * Warning: Invalid argument supplied for foreach() in text_field_formatter_view() (line 273 of /var/www/../modules/field/modules/text/text.module).

Anyone else experiencing this?

The error that is occuring is
parse error: syntax error, unexpected '<' i
sites/all/modules/taxonomy_manager/taxonomy_manager.install on line 45. I am wondering is the a corruption of the database or the file system. I would be pleased to hear what you think will be an adequate solution.
Either to use a backup or fix the modules with this occuring error.

Scaricato l'aggiornamento richiestomi non riesco ad installarlo, in nessun file scaricato esiste un file setup o exe.
Quindi quali file devo usare per l'installazione?
Grazie,
Staff Magnifika