I am assuming this is where we're finding the error. Your description for Events does not seem to match what we need to do. If Gathering Place was removed or changed to another option, feel free to refresh the description as I'm dumfounded here as to what needs to be done to get someone else able to post an event on the event calendar.
However, you must set that parcel to show up in Find Places as a Gathering Place. If your parcel is not set up as a Gathering Place, the parcel will not be available to your friends, but will continue to be subject to other availability rules.
To further clarify, you may post an event on a parcel if:
You personally own the parcel and is at least 512 square meters in size.
The parcel is owned by a group that you are a member of, and is at least 512 square meters.
The parcel is in a private island that you are on the access list of, and is at least 512 square meters.
The parcel belongs to Governor Linden and is set to show in Find Places as a Gathering Place.
The parcel belongs to a friend, it is set to show in Find Places as a Gathering Place, and is at least 512 square meters.
To further clarify, you may post an event on a parcel if:
You personally own the parcel and is at least 512 square meters in size.
The parcel is owned by a group that you are a member of, and is at least 512 square meters.
The parcel is in a private island that you are on the access list of, and is at least 512 square meters.
The parcel belongs to Governor Linden and is set to show in Find Places as a Gathering Place.
The parcel belongs to a friend, it is set to show in Find Places as a Gathering Place, and is at least 512 square meters.