render problem

Hi guys. I have a slight problem when i’m rendering my animation. I have rendered the first 250 frames no problem and can render all frames as active scenes but when I change my render settings to start frame 251, end frame 630 it will not start rendering at 251. Instead it wants to jump to frame 502 or 503. I have attached a screen print jpeg which shows my settings and the actual render. Any help would be greatly appreciated. I have also included a link to my blender file. Kind regards, Paul.

In the Render / Post Processing panel disable ‘Sequencer’