737Ngx Out Of Course Problem!

Hi all

Problem wiht my 737ngx, it's flying his own way when LNAV and VNAV are connected such as COMMAND A. It ownt follow the Purple line on the Navigation display about 70-100NM from T/D (Top of Descent)

It also starts to Descent and climb slowly, like a rollercoaster.

Anyone who has/have the same issue?

Screenshots of my situation:

http://gyazo.com/ded79aad6fcf7201ec3dacf958a7b2da

http://gyazo.com/a0375bd940e5f423b66f522e811dbb3f