It's possible that the Windows machine in question has some registry issues that prevent programs from being uninstalled properly. If that's the case, the iFixit solution provided by Microsoft at https://support.microsoft.com/en-us/mats/program_install_and_uninstall
Alternatively, you can also try to fix this "by hand". Background: The error generally indicates trouble with the Windows Installer's (a Windows component) registration status, it does not necessarily signify any particular problem with Inquisit's installer (i.e., other applications are probably affected as well). Windows Installer program can be re-registered to restore its functionality:
(1) Click Start, click Run, type MSIEXEC /UNREGISTER, and then click OK. (It may look like nothing happened; this is normal.)
(2) Click Start, click Run, type MSIEXEC /REGSERVER, and then click OK. Even if you do this correctly, it may look like nothing occurs, or you may briefly see an hourglass.
After that uninstalling applications should work properly again. Hope this helps.