Invalid argument supplied for foreach()

System:
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PHP 4.4.1
Apache 1.3.34
Drupal CVS-HEAD
Postgresql 8.0.4

Problem:
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If I create a forum and an entry in it, everything looks/works ok. But if I try to 'edit' this entry I get a long list with this error and nothing more.
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warning: Invalid argument supplied for foreach() in /home/erl/drupal-cvs/includes/form.inc on line 233.
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Thanks for your time.