Problem with frame rate - animation

[Radace]

I got problem with animation all was okey but now my framerate in animation is messed up
is like 1-6 frames are ok, then looks like 7 frame make "jump" to 8... and then next 6 frames are ok and again one skipped and jump...

looks like: 1,2,3,4,5,6, 8 , 9,10,11,12,13,14, 16, ......

animation has 25fps, and simple camera transport from point A to B linear speed.
anyone?