So there have been two occasions I’ve run into this error on a page – and it’s very ambiguous and hard to track down both times I’ve experienced it.  Fortunately, both times have also involved a very easy solution once I looked through the page for the 40th time.  The first time I encountered this, the previous form designer had named both cfforms on the page the same thing.  While this worked, it’s never advisable.  By doing this, the cfcalendar script could not locate the item because it couldn’t track down the form properly.

The second time I ran into this – just a few moments ago – was the same problem surfacing because the declaration for the form had been placed inside the declaration for the table.

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<table>
         <form></form>
</table>

This just did not sit well with the browser, being invalid and all.  Once I moved them outside of that formation and made it this:

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<form>
      <table></table>
</form>

it worked like a champ.    Hopefully this helps someone out there with this error in the future!