Errors posting Forum topic

Env: xamp on XP with Mysql 5.0.15-nt, Apache 2.2.0., php 5.1.1, Drupal 5.0.0(CVS)

I'm getting the following errors trying to create a forum topic:

Right after submitting I get a blank screen with:
Fatal error: Cannot unset string offsets in C:\Program Files\xampp\htdocs\drupal5\modules\taxonomy\taxonomy.module on line 751

Then these message in the error block when going back.

* warning: Invalid argument supplied for foreach() in C:\Program Files\xampp\htdocs\drupal5\modules\forum\forum.module on line 371.
* warning: Invalid argument supplied for foreach() in C:\Program Files\xampp\htdocs\drupal5\modules\taxonomy\taxonomy.module on line 729.
* warning: Invalid argument supplied for foreach() in C:\Program Files\xampp\htdocs\drupal5\modules\forum\forum.module on line 345.