nRF24 and MIRF library not working

Hi,
i'm trying to use the library nRF24 and the library MIRF that I got here:

When I try to compile any example, for example (ping client) I alway got the following errors:

ping_client.pde: In function 'void setup()':
ping_client:39: error: 'Mirf' was not declared in this scope
ping_client:39: error: 'MirfHardwareSpi' was not declared in this scope
ping_client.pde: In function 'void loop()':
ping_client:77: error: 'Mirf' was not declared in this scope

I did not find the root cause.
Can anyone help me on this?
thanks
M