OK you are running legacy code from 2003 and it is looking for the Tools menu which doesn't exist in 2010. It will probably still work as Microsoft built in compatibility but it's not the way!

There's a very basic tutorial on how to add XML to create ribbon entries in 2007/10 on our site here and I have also added some XML to your code.

Download from here and then save as a .ppam AddIn (not .ppa) You will see a new tab "Watermark" Make sure you SAVE to your drive as it may open in read Only mode.