This is the Chrome error. There may be different errors in Firefox /IE, indicating a parsing error.
The initial calendar page may load, but when the user clicks on the arrows or tabs to view different dates or layouts, the error occurs.
This indicates a dis-allowed character has been used in a calendar event title field. For example, an event title might be "Fall Meeting #1". The # character will cause this issue. Some other characters which may cause this error include <>?&/
Alternatively, there may be non-standard data in the date or time fields for an event. Check that all events have real dates and times.