Comment 1 for bug 1417146

This is actually a Windows bug (Inkscape could possibly implement a workaround, though).

To manually work around it:
- Open "regedit.exe"
- Browse to "HKEY_CLASSES_ROOT\Applications\inkscape.exe"
- Delete this key ("inkscape.exe")

Afterwards you should be able to associate SVG files with Inkscape normally.

The reason for the bug is that Windows seems to have problems to differentiate between
 - "C:\Program Files\Inkscape\inkscape.exe" and
 - "C:\Program Files (x86)\Inkscape\inkscape.exe"
Therefore if you had the 32-bit version installed and update to the 64-bit version, the reported behavior occurs.