Rafael, the thread you mention isn't there, but an error listed in this thread:
https://openacs.org/bboard/q-and-a-fetch-msg.tcl?msg_id=0006Jt&topic_id=12&topic=OpenACS%204%2e0%20Design has been fixed. I fixed all the bugs I have found over the weekend, including one that didn't allow you to add an event without a date (all day event). Please use the instructions on the above thread to download via cvs the current up-to-date version of calendar and acs-datetime.