FCKeditor and ajax(sack) (onblur and onfocus)

I am trying to write a script that executes an ajax function when an element has focus and another when it has blur.
So far my script is working perfectly for all 'normal' form elements so I am now trying to get it to work with my FCKeditor instance.

I am using the sack script from Twilight Universe (http://www.twilightuniverse.com/projects/sack/) to help build the AJAX.

I now how to capture an onFocus and onBlur events, so that is not a problem.
FCKeditorAPI.GetInstance('instanceName').Events.AttachEvent( 'OnFocus', onFocusFunction ) ;
FCKeditorAPI.GetInstance('instanceName').Events.AttachEvent( 'OnBlur', onBlurFunction) ;

Where I am having difficulty is at the point of requesting the file (ie ajax.requestFile)
Ajax returns the error 404 not found when requesting the file

For all other uses of the script this error is not returned and all is good.

ALSO, I focus on some random textarea then blur from it THEN focus onto the FCKeditor instance the AJAX scripts works fine without the 404 error. If then I focus again on the FCKedit the 404 error returns.

I hope this is clear.
Any suggestions?