Could you paste the exact text of the error message or a screenshot?
To confirm -- the error occurs at installation time, right? before the program is even finished installing on your computer?
All of my programs use Inno Setup as their installation engine, so it sounds like a problem with that -- but not one i've ever heard of before.
You might try just rebooting, in case some process is preventing the installer from working.
Another option is -- all of my installation setup .exe files are actually zip-compatible self-extracting packages, which means you can actually rename the ClipboardHelpAndSpellSetup.exe to ClipboardHelpAndSpellSetup.zip and unzip the contents manually and put the program wherever you want it (in your documents directory for example) and run it from there, if your computer setup won't allow it to be formally "installed" for some reason.