I have a problem with VNAV & V/S

[jolmos]

Takeoff, reached an altitude of 1500 'on the ground, the AP active and LNAV and VNAV. The first (LNAV) is successfully activated, but VNAV, no. I can not activate V / S. "Mysteriously" to a random altitude, I can activate the VNAV function. When I can not activate VNAV or V / S, light flashing alarm lights orange: A / P - P / RST. Can someone give me a help about it? Thank you in advance.
P / D: When taking off is armed the A / T and TOGO thrust.

[Rodeo]

LNAV and autopilot (CMD) can be selected from 400ft AGL, VNAV can be selected from 1000ft AGL.

 

As they say on Game of Thrones: "It is known."  

Edited June 2, 2016 by Rodeo