NS_ERROR_DOM_SECURITY_ERR

Hello,
I have some problem with my fckeditor, when I right click on my image -> Image Properties, this error pop up in the firefox error console...

Error: uncaught exception: [Exception... "Security error" code: "1000" nsresult: "0x805303e8 (NS_ERROR_DOM_SECURITY_ERR)" location: "http://www.myweb.com/admin/fckeditor/editor/dialog/fck_image/fck_image.js Line: 132"]

Does anybody knows wtf is that?