I recently bumped into a problem with Google Calendar. It wouldn't create new entries, no matter how I tried (direct clicking on timesheet, through the Create button, etc.). It worked perfectly in other browsers.
So I checked Firebug, and saw an XHR entry that was red and loaded very fast (4 ms): https://www.google.com/calendar/static/41160d4e4ae6c0f08ffb15dbc5124b31calendarjs_eventformcompiled__en.js
With no further options I copied the above link (which might change between sessions), and tried to load it, which failed. Then I tried to reload it about 3 or 4 times, when it just loaded!
I headed back to Google Calendar, reloaded the whole page and tried to create a new entry and presto! Google Calendar was working fine again.
I'll pay a beer to anyone who explains what happened (upto 1 beer to avoid financial breakdown).