Hiper is right.
Most likely you didn't install all of the required packages from the Software Series.
A similar situation had happened to me before as well and I wasn't able to recover by running pkgtool. However, you might be more lucky...
Your best bet is to reinstall from scratch.
Take a look at Slackware.org and in the 'book' section it describes what's what in each folder. This is actually refered to as 'Software Series'