Have you configured the router side with the correct ppp encapsulation authentication? and correct username and password?i.e.interface modeencapsulation pppppp authentication chap or papusername johndoe password cisco

I am not an expert at this but I found an interesting cisco document on Radius that I believe answers your question with a yes. Here is the cisco document link:http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/secur_c/scprt2/scra...