This would seem to indicate that some of the SQL statements that get run when you first install Calendar have in fact not run properly.
While not a wide-spread problem this is not the first time it has been reported, although most users never encounter this issue.
I have installed calendar hundreds of times and each time the correct tables with the correct columns are created.
Was your install an upgrade from an earlier version?
The only way this is ever going to get fixed is if a person experiencing the issues tries to run the group of queries used to install/upgrade calendar one by one, noting any errors, also providing their server details. If you fancy doing this Iriggle then perhaps the plugin can be fixed in some way.
Post a reply if you fancy doing this.