Sorry, but you've run across a bug in the tab position saving code, which fails if the "C:\\Users\\wicky\\AppData\\Local\\Red Gate\\.Net Reflector 7" directory doesn't exist.
You can turn off the tab saving by going to
and un-checking the "save tabs when I close Reflector". Once you've closed down Reflector once, the directory will have been created in order to store the configuration information. At that point you could check the option again.