I refer you to the fckgLite playground:
http://www.mturner.org/dwfck/fckgLite/doku.php?id=playground:playground
This page has been re-saved several times. So nothing seems to be corrupted because the page is being re-saved. I attach the most recent copy of fckg/action/edit.php. For your purposes, I don't really think there is any difference; it corrects for a conflict between external images and non-image mime types, both of which use curly braces {{. . .}}
Just to make sure that we are on the same page:
1. the xls files which you are attempting to access--are they in the data/media directory?
2. did you create the test files with fckgLite? this shouldn't really matter, but maybe it does.
3. I am testing u sing the current dokuwiki release candidate; maybe this makes a difference--it shouldn't but maybe.
Myron