Do you get this message with multiple programs when you try to uninstall them?

It's possible that you have a corrupt or missing file for the program.  You may have to manually uninstall it if you cannot uninstall it normally.   One trick around this is to reinstall the program ontop of itself, then uninstall it.

Also, as far as more disk space, nowadays it really doesn't cost that much to get another disk.  I just got a 200GB hard disk for only $60 (and the one I got was from the store and brand new).   I am sure you could find a 40GB or 80GB for around $20 on ebay.

Install.LOG is just a text file that programs create as a reference when you install them. They need the info for a complete uninstall.

It is likely that that either the log file has been deleted at some time, or it is stored in a folder where the uninstaller doesn't look for it.

You have two options:

(1) Reinstall the program(s) affected as has already been suggested.

(2) Do a search for '*.log' and see if you can locate log files hiding somewhere. Then shift them to where Windows is looking for it.