I've recently updated to KDE 3.2.3 on my Slackware 10, with security updates. After the upgrade I've tried to add new fonts via the KDE => Control Center => System adm. =>font installer.
but recieve the following error message:

The diagnostics is:
Library files for "libkcm_fontinst.la" not found in paths
Possible reasons:
An error occurred during your last KDE upgrade leaving an orphaned control module
You have old third party modules lying around.
Check these points carefully and try to remove the module mentioned in the error message. If this fails, consider contacting your distributor or packager.

I've totally re-installed kde and in particular kdebase-3.2.3-2, but without any improvement.

Has anybody else experienced this problem?

No, not sure what to tell you........I put KDE 3.2.3 compiled from source on my LFS system and it works fine...........