Error on saving class details.

All of our ENGL1301 courses are having this issue. When any course data whatsoever get changed or altered (maintain schedule of classes) and we try to save the page, it gives this message:

'Data being added conflicts with existing data. (18,2)

When adding a new item to the database, the system found a conflicting item already exists.

This problem can happen if another user has entered similar information at the same time as you. Note the changes you have made, cancel the page, then retry your changes.

If the problem persists, it may be because of an application or other programming error and should be reported to technical support staff.