Hi,
I assume the design of the application note does work.
So: What´s the difference between the Application note and your design?
Clock source, clock frequency, power supply, PCB layout, reset source, I/O configuration, code...?
Klaus
Added:
"severe problems" is not descriptive and therefore useless.
Imagine: I have severe problems to visit my grandmother. Because my grandmother is dead, or does she live far away, or mabe I don´t have the money, or I´m in prison....
--> give a more detailed description of what you expect and what you see instead.