I don't have time to give you a tutorial on the Windows registry (if I even knew enough to do so!), so you may want to do some research yourself. Suffice to say that every aspect of operating your computer and all its installed applications is directed by the registry. Editing it manually is sometimes useful, but one wrong move can hose an application, or the entire computer. The registry editor is "regedit.exe" (clever name, huh?).
The registry is a hierarchical structure, sort of like folders and files on your hard drive. Just be careful not to change anything that you're not sure of. But you can delete the key noted above (Version 17.0) and Inventor will re-create it the next time you run it.
