I am glad I was able to help you. About your problem, that is indeed very strange. Which OS are you using? Did you move the pd-extended folder after installing it? All these libraries are located inside a folder named "extra", which is by default on Pd's path (meaning that they should automatically load when pd-extended opens). I would suggest that you try installing pd again, since this is a very simple procedure and it may be much easier and faster than troubleshooting what is wrong with your install.
And just to be sure (silly questions, but you never know...): are you sure you are typing the name of the objects correctly, including any capitalization? Are all extended objects affected, only some libraries or only some few objects inside a library?
Take care and good luck,