Rendering Problem : It get stuck on a specific frame

Hello,
I'm experiencing a rendering problem that I never had before.
I don't have the strongest computer but so far I manged to render some BIG videos that I created.
When I rendering BIG videos, I'm keeping an eye om the task manger ,etc.

The thing is that now , for some reason , the rendering process get stuck on a specific frame (1594).
The rendering process until this frame, is going pretty fast.
I tried to "trick" the computer and render from frame 1594 to the end , but still...when the process gets to frame 1594 (on the second part - which is frame 3188 if I'm rendering it normally), it's still get stuck.

Is anybody familiar with this issue?

I'm using Sony Vegas Pro 9

Thanks.