This is actually a general problem with all KDE3.5 apps under KDE4.
The issue appears to be that there are separate directories /usr/share/applications/kde and /usr/share/applications/kde4, and the desktop files construct separate sycoca files. Since kfmclient.desktop is only installed in the kde4 directory, the KDE 3.5 apps can't find it in their sycoca.
A simple fix is just to make a symlink from the kde4 file into the kde directory. I.e:
cd /usr/share/applications/kde
sudo ln -S ../kde4/kfmclient* .
kbuildsycoca
and the problem disappears.
I will be filing a bug against Konqueror for this, but it afflicts all KDE4 services in KDE3.5 apps.
This is actually a general problem with all KDE3.5 apps under KDE4.
The issue appears to be that there are separate directories /usr/share/ applications/ kde and /usr/share/ applications/ kde4, and the desktop files construct separate sycoca files. Since kfmclient.desktop is only installed in the kde4 directory, the KDE 3.5 apps can't find it in their sycoca.
A simple fix is just to make a symlink from the kde4 file into the kde directory. I.e:
cd /usr/share/ applications/ kde
sudo ln -S ../kde4/kfmclient* .
kbuildsycoca
and the problem disappears.
I will be filing a bug against Konqueror for this, but it afflicts all KDE4 services in KDE3.5 apps.