Ben, calendar requires acs-datetime 4.0 and I think APM is looking at the version rather than the
tag and 4.0b2 < 4.0. I will
check if that is in fact the case. I saw this on the install I did yesterday.
From the calendar.info file...
<version name="4.0b2" url="https://openacs.org/apms/acs-datetime-4.0b2.apm">
<provides url="acs-datetime" version="4.0"/>
