Error in vid.CurrentTime: Expected CurrentTime to be a scalar with value <= 0.

I wrote a simple function to read specific frame or a sequence of frames from the video using "readFrame" instead of read since Matlab is phasing "read" out. From time to time I get the following error:

 Error using read_frame_video (line 4)
Expected CurrentTime to be a scalar with value <= 0.

I know I'm trying to assign a negative value to CurrentTime property since I'm printing them out. What else could be the source of this error ?

Here's my function: it just reads either one frame or a sequence of frames same way as read used to.

 function mov = read_frame_video( vid, frame )
if length(frame)==1
    beg=(frame-1)/vid.FrameRate
    vid.CurrentTime = beg;
    mov=readFrame(vid);
    return;
elseif length(frame)==2
    if frame(1)<=frame(2)
        beg=(frame(1)-1)/vid.FrameRate;
        vid.CurrentTime = beg;
        I=readFrame(vid);
        mov=uint8(zeros(size(I,1),size(I,2),size(I,3),frame(2)-frame(1)+1));
        mov(:,:,:,1)=I;
        for i=1:frame(2)-frame(1)
            mov(:,:,:,i+1)=readFrame(vid);
        end
    else
        display('Incorrect frame indexing');
        return;
    end
elseif length(frame)>2
    display('Array frame has more than 2 elements');
    return;
end

end