hmm method="POST" is in the default template, so if it hasnt been modified it shouldnt be the culprit. though to check, when you submit the choice, on the page with the error - is there anything after ultimatebb.cgi (like ultimatebb.cgi?ubb=...) or is it just ultimatebb.cgi? have you modified public_top_topic.pl?
also, does bumping the topic work? i assume this is a 6.2.1 right?
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