This means you have v0.78 and v0.79 installed at the same time, it's a known issue just in this new release, you have to manually uninstall v0.78, check the note in here:
http://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html
http://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html