Installing Eraser on top of another version (especially if it was Eraser 5) almost always creates trouble. You don't say precisely what error you are getting when you try to reinstall, but I suspect that probably doesn't make much odds.
You will definitely still have a conflict with some remaining element(s) of the original installation. In my experience, these can take a bit of work to remove. The problem is not with the Eraser code and data, which is quite tidily arranged. What tends to cause trouble is the material (particularly registry values) that the Windows installer happily secretes throughout the system.
You need to do what I call a 'brute force' uninstall. If there is an uninstaller, run it. Then, whether or not you have run the uninstaller, manually remove all traces you can find in the file system and the Registry. Make sure your folder options are set to allow viewing of hidden files and folders. Places to look in the file system are the Program Files folders (delete any Eraser folders completely), and the C:\Users\<Your User Name>\Appdata\Local folder, where there may be a folder named 'Eraser 6'. Then use the Registry Editor to search the registry on 'Eraser' and delete all keys and values that appear to be Eraser-specific. Reboot (this can be important). Then re-download Eraser and reinstall.
If this does not work first time, keep at it. Apart from a broken install blocking the re-installation, the only other possibility is a problem with the Windows Installer itself. But, to my mind, this seems unlikely with the error message you had.
David