Did you at any time delete or move the install.log files relating to the programs that you want to uninstall? They tell uninstall what to remove, including files and registry entries. Look in the relevant folders of the programs in C:\program files (assuming that is where you installed the apps). Not all applications use them, but presumably the ones you want to uninstall do, or they would not be asking for their install.log. If the file is present, then it is probable that the registry uninstall information has got deleted or corrupted. If the file is missing, then that is obviously the cause for the failed uninstall.

The first thing I would try is to reinstall the program(s), which might restore the install.log and registry entries. That does not always work, but might be easier than trying to fix the registry or do a manual uninstall, which are the two other options.

The second strategy, if the file is present, is to check the registry.

Using regedit, navigate to 

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\programname

where programname will generally be recognisable as relating to the program of interest. In some cases the key name is a long string of numbers, but if you click on one of those, in the right pane you will find what software it relates to.

In the right pane for the relevant key there should be a string value called UninstallString and its data includes the path to the install.log file (in DOS naming convention for folder names greater than 8 characters).

Example, I have Adaware in C:\Program Files\Lavasoft\Ad-aware 6. The registry key for uninstall information is

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Ad-aware 6 Personal

The data for the UninstallString is

C:\PROGRA~1\Lavasoft\AD-AWA~1\UNWISE.EXE C:\PROGRA~1\Lavasoft\AD-AWA~1\INSTALL.LOG

If the UninstallString is not there, but the install.log file is in the program folder, you could try to create the value. The first part refers to the program's uninstall.exe, the second part to the install.log

If the whole uninstall key for the program is missing, or if the install.log file is missing for a program that requires it, then the only remaining option would be a manual uninstall, including cleaning up the registry manually (or using a registry cleaning tool such as regscrubXP or jv16 Power Tools). Looking at the program's .inf file if there is one (it contains the details of files loaded and registry entries made during installation, and can be read in Notepad) is useful for manual uninstall.

If reinstall does not work and you don't feel comfortable about editing the registry and you want more guidance on manual uninstall, please post. It would be helpful if you could state which programs you want to uninstall.