Features / Usability

I am a new user & have just upgraded to 3.0 and when I try to save a calender item I recieve the error shown below:-
I am logged on as the default admin user.
I was getting the same error in 2.4 & something similar when trying to create a structure.(I was hoping the upgrade would make it go away)
I've noticed that 'Structures' is not included in main menu now.(Company intranet Profile).
My questions are:-
How do I fix this error ?
Would it be related to the 'Structure' error. ?
Do 'Structures' still exist and are just not included in Company Intranet Profile ?

Any help much appreciated.

Error

An error occured in a database query!

Context:
File tiki-calendar_edit_item.php
Url tiki-calendar_edit_item.php
Query:
INSERT INTO `tiki_calendar_items` (`user`,`calendarId`,`name`,`description`,`status`,`url`,`lang`,`allday`,`start`,`end`,`priority`,`locationId`,`categoryId`,`nlId`,`recurrenceId`,`lastmodif`,`created`) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)
Values:
0 admin
1 1
2 Staff Metting
3 Monthly staff meeting
4 1
5
6
7 0
8 1244080800
9 1244084400
10 0
11 0
12 0
13 0
14 NULL
15 1244007156
16 1244007156
Message:

Built query was probably:
INSERT INTO `tiki_calendar_items` (`user`,`calendarId`,`name`,`description`,`status`,`url`,`lang`,`allday`,`start`,`end`,`priority`,`locationId`,`categoryId`,`nlId`,`recurrenceId`,`lastmodif`,`created`) VALUES ('admin','1','Staff Metting','Monthly staff meeting','1',,,'0','1244080800','1244084400','0','0','0','0',NULL,'1244007156','1244007156')