Problem building with mock

[Eric Tanguy]

When i build a package locally using rpmbuild -bb foo.spec the package
build fine when i try to build it using mock foo.src.rpm the building
failed : 

lines building mock : 
make[2]: Entering directory `/builddir/build/BUILD/drgeo-1.1.0'
/bin/sh ./mkinstalldirs /var/tmp/drgeo-1.1.0-8.fc5-root-mockbuild/usr/bin
  /bin/sh ./libtool --mode=install /usr/bin/install -c
drgeo /var/tmp/drgeo-1.1.0-8.fc5-root-mockbuild/usr/bin/drgeo
/usr/bin/install -c
drgeo /var/tmp/drgeo-1.1.0-8.fc5-root-mockbuild/usr/bin/drgeo
LC_ALL=C ./intltool-merge -d -u -c ./po/.intltool-merge-cache ./po
drgeo.desktop.in drgeo.desktop
/bin/sh ./mkinstalldirs /var/tmp/drgeo-1.1.0-8.fc5-root-mockbuild/usr/share/applications
mkdir -p
-- /var/tmp/drgeo-1.1.0-8.fc5-root-mockbuild/usr/share/applications
 /usr/bin/install -c -m
644 ./drgeo.desktop /var/tmp/drgeo-1.1.0-8.fc5-root-mockbuild/usr/share/applications/drgeo.desktop
/usr/bin/install: cannot stat `./drgeo.desktop': No such file or
directory

same lines building locally : 
make[2]: Entering directory `/home/tanguy/rpmbuild/BUILD/drgeo-1.1.0'
/bin/sh ./mkinstalldirs /var/tmp/drgeo-1.1.0-8-root-tanguy/usr/bin
  /bin/sh ./libtool --mode=install /usr/bin/install -c
drgeo /var/tmp/drgeo-1.1.0-8-root-tanguy/usr/bin/drgeo
/usr/bin/install -c
drgeo /var/tmp/drgeo-1.1.0-8-root-tanguy/usr/bin/drgeo
/bin/sh ./mkinstalldirs /var/tmp/drgeo-1.1.0-8-root-tanguy/usr/share/applications
mkdir -p -- /var/tmp/drgeo-1.1.0-8-root-tanguy/usr/share/applications
 /usr/bin/install -c -m 644
drgeo.desktop /var/tmp/drgeo-1.1.0-8-root-tanguy/usr/share/applications/drgeo.desktop
make[2]: Leaving directory `/home/tanguy/rpmbuild/BUILD/drgeo-1.1.0'


I can't understand why there is a problem with mock. Someone could
explain me ?
Thanks

Eric