Do you know why this script does nothing?

[Zbigniew Luszpinski]

for f in "`find . -name DETAILS`"; do
    sed -i -e 's at ftp://ftp.x.org/pub/X11R7.0/@$XORG_URL/X11R${VERSION}/@g' 
"$f" > /tmp/tymczas;
    mv /tmp/tymczas "$f";
    done

This script should find all DETAILS files in xorg-7.0 and change url patch. 
None of files are modified. What' wrong with it?

I tested for - returns correct files. Then checked sed, replaces strings. 
Finally checked mv, moves files. Everything works. When all these commands 
are put together in one script everythng works except that none of files are 
modified. Arrgh!

zbiggy